A senior member of Boris Johnson’s administration today resigned after “discrepancies” emerged over the use of his corporate credit card.

Ian Clement, the Deputy Mayor for Government and External Relations, resigned after an internal investigation at City Hall raised concerns over the “veracity of his claims”.

It is understood that City Hall officials found a discrepancy over a restaurant meal that was claimed as corporate expenditure. It is believed that the person who Mr Clement named as his companion was not present at the meal.

The resignation came only days after Mr Johnson, who has lost several deputies since he won office last year, supported Mr Clement publicly over other issues that had been raised about his use of the card.

Mr Clement had already admitted to a “crass mistake” and had been reprimanded by the Mayor after he used his card to buy personal items on the public purse, directly violating Greater London Authority rules.

His credit card was withdrawn after it emerged that he had used it for restaurants, supermarket shopping and upgrades to business-class flights.

Mr Johnson refused to accept his resignation because it appeared that Mr Clement, the former leader of Bexley Council, had paid back all the money back before the misuse was discovered.

Mr Clement resigned today after further discrepancies emerged.

Although he has recently enjoyed a reprieve from controversy, Mr Johnson suffered a series of resignations in his first year as Mayor of London.

Ray Lewis, the Deputy Mayor for Youth at the centre of the fight against knife crime, resigned after he was forced to deny allegations of inappropriate conduct and financial irregularities in his past. James McGrath, the mayor's senior political strategist, left over a race row and Tim Parker, the high-profile businessman, resigned only weeks after taking up his post as chief of staff.

David Ross, the Tory tycoon and co-founder of Carphone Warehouse, also quit in as Mr Johnson’s senior Olympics adviser in December when he became embroiled in a shares scandal.

In a letter to Mr Clement today Mr Johnson said: “As you know, I was extremely angry at the liberties you took with your corporate credit card; but last week I made the essential distinction between behaviour that is crass and anything that amounts to dishonesty or deception.

“In the light of the further discrepancies in your expenses that have emerged this morning, it is clear to both of us that your position is untenable.”

Mr Johnson thanked Mr Clement for his “hard work” in the past year.

In reply, Mr Clement wrote: “It has been a pleasure to work for you and I am sorry that I have let you down and deflected away from the excellent work you, and indeed your team, are doing in delivering for Londoners.”

Jennette Arnold, a Labour member of the London Assembly, said: “Ian Clement’s repeated misuse of his City Hall credit card was clearly a serious breach of Greater London Authority rules for which he has answered with his job. However, Mr Clement’s resignation cannot be considered an end to the matter.

“Serious questions remain about how long the misuse of the card continued, apparently undetected, and the type of expenditure that was charged to the GLA without being repaid.”

Ms Arnold is the chair of the London Assembly's business management and administration committee, which will review Mr Clement's expenses on Wednesday.

A spokesman for Mr Johnson said that his approach to the issue had been "open minded and fair".

He insisted that the loss of a string of deputies did not reflect on Mr Johnson's leadership, who had "taken a chance" on hiring people from diverse backgrounds.

"How could we possibly pre-empt this kind of thing? Ian Clement had a lot of experience in local government and has a result had been under intense scrutiny."

Times Recommends

• Shrinking violet Gordon turns into raging bull
• Eddie Izzard: 'I keep thinking if I do all these things she'll come back'
• Is sex for the disabled the last taboo?