Speaking to the Sunday Telegraph, the Edinburgh MP revealed how he was shocked to discover that RBS was on the brink of crashing down and causing shockwaves throught the economy.
Mr Darling feared the knock-on effects on the British economy and banking system if the bank had gone under, and the crucial information came in a phonecall.
“The scariest moment was when the system could have collapsed,” Mr Darling said.
“Tom McKillop, who was then the chairman of RBS, phoned me up to say the bank was running out of money. When I asked him how long he would last, he paused and said ‘Well, maybe two or three hours’.
“This was then the largest bank in the world. I just closed my eyes and thought ‘What if they close the doors and shut down the cash machines?’”
RBS was eventually bailed out by the government, with 82 per cent owned by the taxpayer.