Is London to Brighton's Balcombe rail tunnel safe?

Two years ago, part of the roof of the Balcombe tunnel on one of the busiest commuter routes in the UK collapsed.

The tunnel was immediately closed, but a subsequent Rail Accident Investigation Board report concluded passengers' lives had been put at risk.

Three metal girders had come loose and were found to be hanging less than a foot from the top of the train.

Mark Norman investigates the partial collapse on the London to Brighton line and speaks to a Network Rail engineer who claims passengers could have died.

Network Rail says it has re-engineered the tunnel to make sure the risk has been removed and it has instigated a more rigorous inspection regime.

Inside Out is broadcast on Monday, 30 September on BBC One South East and South at 19:30 BST as well as South East Today. The full film can also be seen nationwide for seven days after transmission on the iPlayer.