Mission which circled saturn for 13 years, sending back never before seen images. Good evening and welcome to bbc news. An explosion on a tube train in south west london this morning is being treated as a terrorist attack. Witnesses have spoken of a flash and a bang and then panic as commuters ran out of the carriage. 29 people have been treated in hospital, some suffering from burns. The incident happened in the morning rush hour as a District Line tube train pulled into the overground station at Parsons Green in south west london at 8. 20am. The bbc understands that the bomb, described as a homemade device, had been fitted with a timer, but it failed to fully detonate. Whoever planted it is still on the run. Tom symonds has our first report tonight. At 8. 20am, the friday commute was well under way. A packed commuter train, young, old, children, pensioners, everyone. At Parsons Green station, where the lines run overground, a brief stop. I stepped on and within two seconds, a massive bang. Loud enough to make me wonder what it was, and i looked around and this wall of fire was coming towards us. I turned and i saw the fireball surged towards my side. You heard the loudest, scariest screams coming from what sounded like the carriage next to us. People shouted run, so we ran for our lives. It was pandemonium on the platform, people falling down because everybody was trying to make an exit. It was pandemonium on the platform, people falling down because everybody was trying to make an exit. I fell over somebody who had fallen in front of me but managed to get myself up. A passing passenger pointed a phone back at the train. Inside was this, still flaming, a white bucket with something inside. Police later confirmed a makeshift bomb. Get away and move down the platform. Despite the explosion, the train appeared in tact, although the line was brought to a halt and other trains is that you to as passengers were to safety. Hundreds were able to walk away, uninjured. But not all. On the street, the Emergency Response was under way. I have seen a woman stretchered off, and clearly her legs are wrapped up and she had burns to herface. She is conscious, she was taking some oxygen and pain relief, as well. But clearly, people have sustained very nasty burns. 29 people have been injured, most suffering from what Police Describe as flash burns. Move back, thank you. The area around the station was cleared, sniffer dogs checking nothing was left to cause further harm, and another terrorism operation got under way. The investigation is being led by the metropolitan Police Counterterrorism command and part of the National Terrorism policing network, and there are urgent enquiries, with hundreds of detectives looking at cctv, forensic work and speaking to witnesses. That work starts here. The first urgent task, to identify whoever put the bomb on this train. The advantage for the police is that these trains have cctv cameras, as do the platforms. They also have the device pretty much intact, and its packaging. And they will also look for anything dropped by the suspects, which has happened in the past. Beyond here, the Intelligence Services will want to know who did this, who they are in touch with, and whether anything else is planned. The governments Emergency Committee decided not to raise the National Threat level, suggesting no further imminent attack has been detected, but security is being stepped up, again. People travelling in london will see an increased Armed Police Presence on the transport network, and they will see security increased, and the police will do what is necessary to protect the public. There were injuries, but no one was killed today. This could have been a lot worse. Yet a bomb was placed unnoticed on the tube, demonstrating that warnings to be vigilant should not be ignored. Im just reading the reports coming out of cairo that is saying so called Islamic State has claimed responsibility for that blast and reuters reporting the militant groups newsagency. So, so called Islamic State claiming responsibility for the blast. We will await further verification of that if and when it comes. Lets speak to helena lee, who is near the scene in south west london. Bring us up to date on events there this evening. What has been described to me by someone who works close by to hear is that this is normally have very quiet family area, but tonight to nearly 12 hours since that incident took place there isa since that incident took place there is a huge amounts of Police Activity here this evening. We are at the cord and. Just behind us in the distances Parsons Green tube station and we can see what we believe to be the tube train involved in that incident earlier on during rush hour this morning, at around 8 20am. What is going on here this evening is forensic officers have been going through the carriages of that train where the device was detonated this morning. They have been scouring the area for clues and we understand that the device is still on the train. six teams do not want to do is rush that. They want to make sure that the devices made safe before it is moved, but also, crucially, it will have a huge amount of clues for them in terms of trying to track down who put that device on the train. So, there are a lot of police here. We expect them to remain here overnight while the investigation continues, but as well as that, we have also got the search for the person who put the device on the train, questions that officers will be trying to establish our wedded the person get on . Which station . Specialist cctv officers will be scouring hours and hours of footage to try to trace the person. The device was put into quite a visible supermarket died. It will be fairly easy for detectives to try to trace people get onto that train. A big job ahead for officers and we are expecting to hear from Scotland Yard this evening with an update on how that investigation is going. Thank you for the time being. We are expecting something more from scotla nd expecting something more from Scotland Yard. We will bring that to you. The head of Counter Terrorism says hundreds of detectives are now involved in the investigation. The bomb is being examined by forensic teams and officers are looking through cctv at the station for clues about who planted it. Our security correspondent Gordon Corera takes a closer look now at the investigation and where it might lead. This device is at the heart of the investigation, and it will have provided police with many clues. One clue are the wires coming from it, almost certainly used to try to trigger an explosion. They look similar to these Christmas Tree lights that a birmingham man planned to use in a home made device before he was arrested. Such improvised devices do not always go off properly. That was the case on the 21st ofjuly 2005 when the underground was targeted. Experts believe todays bomb also did not explode as intended. The size of the device employed was quite significant. Had it functioned in its intended and designed mode, we would have seen considerable casualties, many people injured, probably many killed. The explosive may have been a compound called tatp. This footage from Brussels Airport and metro shows the devastation when it detonates properly. More than 30 were killed. It is also thought to have been used in the Manchester Arena attack this year, which involved a suicide bomber. But todays attacker wanted to get away, and used a time. Away, and used a timer. That is similar to damon smith, seen here leaving a timed device at North Greenwich a year ago, which was spotted before it went off. Today, hundreds of Counter Terrorism detectives have been employed in this investigation. They have been forensically analysing this device, looking for fingerprints and dna. They have also been scouring cctv images, looking for an individual carrying this bag onto the tube and then getting off without it. That will have been the starting point for their manhunt. Mi5 are assisting the investigation. So far, officials have expressed caution about identifying a motive but they will want to know if the attack was part of a group, or acted alone. And, as has often been the case recently, if they were previously known to the authorities. Unfortunately, it would not be surprising. The concept of a lone wolf now would more accurately be described as a no wolf. Described as a known wolf. Increasingly, attacks have been committed by individuals who were known in some way to either the Counter Terrorism police or mi5 beforehand. 0fficials here have reacted with irritation to this tweet from donald trump. Another attack in london by a loser terrorist. These are sick and demented people who are in the sight of Scotland Yard. Must be proactive. Theresa may responded that it was never helpful to speculate about an ongoing investigation. For the fifth time this year, the country is dealing with the aftermath of a terrorist attack. This one could have been worse, but the urgent priority now well be finding whoever left the device, and making sure they pose no further danger. Gordon corera, bbc news. We were talking about a packed commuter train. Some eyewitnesses spoke of panic and pandemonium. We are nowjoined by dr chris cocking, senior lecturer in the department of psychology at the university of brighton. He has done quite a bit of work and how people react as a group when things like this happen. When you look at how people have reacted here, hong typical how typical was this . They were reporting that there was panic. What we have found we studied maths emergencies, mass panic is pretty much entirely a myth. Crowds behave in a much more orderly way than is often expected. People clearly want to get out and away from the danger, but they very quickly move on from that, is that what youre saying . Sure. And to flee quite quickly from a life threatening incident is not panic, it is logical. That is why we reject the use of the terms because it implies people act selfishly, they trample on people. Our studies have found that doesnt happen. If people are able to cooperate they will and if they can pick up people who fall over, they do. So they will look to help others very quickly after the initial shock . Yes, almost instantaneously. Research i have done has found that even when crowds are fleeing a threat they will help other people while they are in flight. Other people while they are in flight. The psychological point here is that here was a tube train full of people who didnt necessarily have any reason to be communicating with one another, invariably people dumped in london on a typical morning, suddenly they have something horrific in common. Exactly. That is what we find very interesting, when the physical crowd becomes a psychological crowd. People who previously would not even speak to each other, the social norm on an normal tube date is you dont speak to each other, but when defining incident happens like this, people cooperate and behave in very selfless and altruistic ways. We would say it is a good example of a psychological crowd in this situation. And will continue to do so situation. And will continue to do so in giving police the information they might need, presumably. Crowds are very resilient, but after the event people provide social support. The recent tragedy at Grenfell Tower has shown that the community has come together and often the narrative is used that london can ta ke narrative is used that london can take these things, we have the blitz and the ira campaign, and people do support each other. You see tremendous act of altruism. People today were offering free cups of tea and things like that. People can be remarkably altruistic. What about the longer term impact . The people affected this morning will need to ta ke affected this morning will need to take underground train journeys in the coming days. What kind of impact can this have as people look forward to that in the coming days and weeks . There can be an effect on the people to be more anxious were vigilant. The people to cope remarkably well. This happened after 77. People using the tube that they went back to using the tube afterwards. Very good to have your thoughts. Thank you very much indeed. Joining me now via webcam is simon adcock, who is the vice chairman at the British SecurityIndustry Association and who works closely with the Governments National surveillance camera strategy. Good evening to you. Clearly, this cctv footage here will be vital. Yes, absolutely. Im sure the priority of the police now will be to prevent further harm and to this end they will be looking to locate not just the bomber end they will be looking to locate notjust the bomber but end they will be looking to locate not just the bomber but any accomplice must. Cctv evidence will play a vital role in that. The first job they have got is to collect all the footage then they have a huge task to analyse at all. It is a huge task to analyse at all. It is a huge task when you think about the hours they will have to go through. Task when you think about the hours they will have to go throughm task when you think about the hours they will have to go through. It is. They already have an image of the bomberfrom the they already have an image of the bomber from the footage on the train so bomber from the footage on the train so they know what time it was left there. There will be looking to see when that person gone off and off the train and there will be tracing their movements through the station. Clearly, the people who perpetrated this may have done it in disguise, but there are experts who can perhaps get through that . Thats right. In the 2011 local riots there was a group of people known as super recognisers. These are human individuals in the top 1 or 2 from facial recognition tests. They can recognise people from very small signs. It is things that asked normal human beings wouldnt be able to do anything with. What about the level of cctv coverage now in london and another major cities around the uk, how do we compare . The uk is acknowledged as being one of the leaders in camera deployment and also regulation. We do have one of the highest numbers of cameras per head of population in the world. In 2013 nastily find that there were 5. 9 million cameras in the uk. It sounds a lot. Some people say it is too many. Yes, of course. The vast majority of those cameras come over 90 , are on private property is in store by private businesses to protect their assets. Do we have too many cameras . If we have no security threats, then absolutely. When there isa threats, then absolutely. When there is a serious crime committed they are an invaluable tool. In 2009, many of the Scotland Yard murder cases used cctv evidence. There is a balance to be struck between security and privacy. That is the aim of the National Surveillance camera strategy to make sure we dont lose that support from the public who feel they are being spied upon. Thank you very much indeed for coming on. 29 people are injured after an explosive device is detonated on a packed tube train in london. 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