MailOnline understands that complicated cases are taking 40 minutes rather than the expected four minutes Only half of desks can be used in passport control at Heathrow because they only have front-facing screens Heathrow chief solutions officer Chris Garton said the situation at the west London airport was 'untenable' Passengers are regularly waiting between two and six hours to get tested, he told MPs at a select committee Mr Garton said the Home Office has not increased the number of border staff checking arrivals to Heathrow