TWO passenger trains came within minutes of disaster when part of a tunnel collapsed at Gerrards Cross.

Dozens of commuters were moments from passing through the tunnel when it caved in and thousands of tonnes of dirt and concrete crashed onto the track at around 7.30pm on Thursday, June 30.

The tunnel is part of a development for a new Tesco store.

The driver of the 5.40pm Chiltern Rail service from Stratford-upon-Avon to London Marylebone was about to depart Gerrards Cross station when he saw a 30-metre stretch of tunnel suddenly give way.

His swift action in raising the alarm allowed another train approaching in the opposite direction to stop just yards from the mountain of debris.

Reg Whittome, chairman of both the Marylebone Travellers' Association and the Chiltern Railway Passenger Board, was amazed no-one was killed.

"There would have been an almighty tragedy had there been a train going through the tunnel at the time it collapsed," he said.

"There was no warning and the fact it didn't happen during the busiest time of the morning is divine providence. Had it been during the rush hour, hundreds could have been killed."

Train timetables have been thrown into chaos since the 320-metre tunnel gave way. Network Rail says it is fully focused on reopening the railway as quickly as possible, but admits the task ahead is "huge" with major disruption likely for some time.