protest against austerity cuts last year and is warning there will be more of the same on april the 29th, which he describes as -- >> a shock and awe campaign. it will involve a lot of fireworks. it will involve a lot of people dressed in black. it will involve a lot of very, very loud music. >> reporter: security expert roy ram shows me the aftermath of the latest protest. >> you see them here doing this kind of damage, which is just completely ridiculous. >> reporter: this is just one window of hundreds. >> absolutely. >> reporter: he says the royal wedding presents an incredibly difficult challenge. >> the police have got a job to get the public in, close up to the wedding, but they've got to keep the people who want to cause disorder and damage like we're seeing here away from the royal wedding. it could be immensely disruptive. you know, it's a very unenviable position the police are in. >> reporter: the big problem for the police is getting evidence to stop the anarchists doing something before they get to the wedding route. there is talk of using stop and search powers.