Abdul El-Gayar, 31, who works on the platform at Cannon Street station, not only prevented a City worker’s bike being stolen but waited at the station for four hours after his shift ended to make sure the bicycle was returned to its owner.
Mr El-Gayar made the intervention as he was clocking off at around 2pm on Wednesday, when he spotted a thief attempting to use a pair of bolt cutters to break the lock of a bike chained up outside the station.
He said: "I heard the sound of a lock being snapped and I didn't think twice. I said: ‘You're not taking that back.’ I couldn't let that happen.”
During the exchange Mr El-Gayar said “voices were raised a little” but that “the guy eventually gave up and walked off”.
The transport worker said he is himself a cyclist and wanted to help out a fellow two-wheel enthusiast.
He said: “I have a bike and cycle to work - I know what value they have to people.
"The guy eventually gave up and walked off. I put the bike into safe storage because the lock had been broken."
The bike owner, Steve Farmer, who works near the station, returned four hours later and realised his bike was missing.
It was the first day back in the office for the 39-year-old from Guildford, Surrey. He usually locks his bike up in the office, but had forgotten his security pass and thought as it was “so dead” around Cannon Street he would get away with using his son’s bike lock rather than his usual D-lock.
He said: “It was the one day I didn't use a D-lock.
"I was gutted. I was annoyed that I had used a bad lock to lock it up with. I was resigned to the fact I would never see it again, but trudged back up to the station, thinking there was no point really in asking for the security cameras but wanted to try anyway."
But the lucky commuter was soon was met by Mr El-Gayar. After entering the correct code into the bike lock to prove he was the owner, Mr Farmer was reunited with his bike.
Mr El-Gayar said: "City people finish work at about 5.30/6pm - it came to 6pm and I was wondering where the owner might be when a young man came through the station.
"He said he couldn't thank me enough. I was only too happy to help - I couldn't let a bike theft happen right in front of my eyes."
Mr Farmer added: "I can't thank Abdul enough, he is such a top man.
"The world needs more Abduls, he is a legend of a man and a credit to his employer."
The attempted theft has been reported to the City of London Police.
Additional reporting by PA Media.