When raiders hit the City of London offices of Sumitomo Mitsui Banking Corporation they did not prepare themselves with weapons and masks. Instead they simply arrived with a list of passwords jotted down on a bit of paper, logged in and attempted to help themselves to Ł229 million.

Had they succeeded, the audacious theft would have topped the record books, dwarfing the Ł53 million Tonbridge cash heist and even a Ł141 million robbery in Baghdad. The men were not foiled by hi-tech security but because they failed to enter the passwords in the correct fields of the unfamiliar electronic banking forms.

Investigators feared the low-key break-in may have never been made public because of the potentially embarrassing consequences for the bank.

Sharon Lemon, director of e-crime at the Serious Organised Crime Agency (Soca), said the first officers at the scene were confronted with little more than vandalised computer terminals. But once the illicit transactions were found the sheer scale of the theft, which involved a complicated network of front companies, quickly became apparent.

Ms Lemon said: "If the bank had not been bold enough to report this - and it was a potentially sensitive incident - we may never have known about it. This was a global investigation and the crime and effort we made to invest in international relations really paid off. It was a complicated technical and financial investigation, all of our techniques were brought to bear to arrest and convict the offenders. It does not really matter where the criminals come from. If they intend to target the UK then it is our responsibility to track and convict them. Organised criminals are not commodity specific, they are money specific and if an opportunity presents itself then they will take it."

Preparations for the raid on the evening of Friday October 1, 2004, began the previous month with three surreptitious visits by a pair of computer experts.

Corrupt security boss Kevin O'Donoghue led the way for Belgian hackers Jan Van Osselaer and Gilles Poelvoorde using security cards belonging to other staff. He also tampered with CCTV cameras and even severed cables at the Queen Victoria Street offices in a bid to prevent the illicit visits being recorded. O'Donoghue later claimed he was threatened and forced to take part but CCTV footage showed him laughing and joking with the two hackers.