Credit card details were collected from more than 8,900 customers

Sunil Mahtani, 26, told London's Middlesex Guildhall Crown Court he felt so frustrated the merchant banker he loved earned more than him, that he teamed up with a gang of hi-tech crooks.

Mahtani, from Watford, Hertfordshire, repeatedly downloaded details of credit cards while working for Checkline plc, the company which processed ticket purchases of Heathrow Express customers.

The details were handed to his partners in the fraud and the information electronically encoded on to cloned credit cards and used to fund spending sprees in the UK and abroad.

Altogether, Mahtani, who pleaded guilty to two counts of conspiracy to defraud, collected information from about 8,970 cards - 10% of them were cloned.

Shaidal Rahim and Shahajan Miah, also 26 and from Enfield, north London, both pleaded guilty to one count of conspiracy.

The credit cards were used to buy cigarettes abroad to sell in the UK

By the time police arrested the three men, bank losses had climbed to more than �2m.

Roger Smart, prosecuting, said: "This is the largest credit card fraud investigated to date by any police force in the UK."

He estimated if the gang not been caught when they were, the financial damage could have reached �20m.

The fraud was quickly discovered by industry investigators and the Heathrow Express connection uncovered.

But after spending more than a year trying to discover the "point of compromise", Scotland Yard's cheque and credit card unit was called in.

In the meantime, Mahtani's partners were using hire cars to tour French and Belgian tobacco stores to buy cigarettes to sell in the UK, the court heard.

Ali Bajawa, defending, said Mahtani was happy in his job until he became more aware of the financial gulf between his wages and those of his merchant banker girlfriend, Elizabeth Ryan.

"It may be that to enhance his sense of esteem or just out of frustration, a lack of job satisfaction, status and income, Mahtani fell prey to temptation," he said.

Mahtani also admitted to charges of making indecent photographs of children and two of possessing them with intent to distribute.