For nearly 40 years, Alton Towers has attracted visitors to some of Britain's most thrilling roller coasters. But in June 2015 something went very wrong. Two carriages collided on one of the park's most popular rides, injuring 16 people, five of them seriously. This one-off documentary goes behind the scenes as the UK's biggest theme park attempts to win back visitors with the launch of their multi-million pound new roller... see more