Late on Wednesday 7 August 1963, a Travelling Post Office train left Glasgow for Euston, with staff on board sorting mail before its arrival in London.
Registered mail, much of which contained cash, was sorted in High Value Package carriage at the front. This post would normally have been worth around £300,000, but there had been a Bank Holiday weekend in Scotland, so the total was £2.3million (around £30m today).
At about 3am on 8 August 1963, moments after passing Leighton Buzzard, driver Jack Mills stopped for a red signal - but it was a fake created using a glove and battery-powered light.
His co-driver David Whitby climbed out of the diesel engine to ring the signalman, but found that the line-side phone cables had been cut. He was then attacked and thrown down the embankment.
A masked man climbed into the train cab and hit Mr Mills around the head with an iron bar, leaving him unconscious.
Others uncoupled the carriages, leaving the engine and the first two carriages.
The steep embankments at Sears Crossing were impractical for removing the money from the train so the gang planned to drive the train a mile further to where Land Rovers were waiting to transport the cash to a hideout.
But Old Pete, who had spent months befriending railway staff to learn to drive a train, realised the huge diesel train was far more complicated than local trains he had previously driven. Ronnie Biggs had to rouse the driver to continue the journey.
Staff left in the ten carriages at Sears Crossing did not realise anything had happened.
At Bridego Bridge, a human chain of robbers removed 120 sacks containing 2.5 tons of cash.
The gang told staff in the first carriage to stay still for 30 minutes before calling the police. This gave investigators an important clue to the whereabouts of the gang's hideout.
They had rented an farmhouse in Oakley, Buckinghamshire, and during the next few days they shared out the cash, playing Monopoly using real money.
A police investigation was launched…