Critics said Ian Clement used City Hall as his personal back account
London Mayor Boris Johnson has been urged to sack one of his advisers caught up in a row over expenses.
Ian Clement, deputy mayor for external relations, said he made a "crass mistake" in running up about £1,500 on a corporate credit card.
The money was spent on groceries and meals out. London Assembly's Labour leader John Biggs has questioned the mayor's judgement over the issue.
Mr Johnson said Mr Clement's use of the card was "absolutely wrong".
He added it was "critical" that the amount was repaid.
Mr Clement resigned as leader of Bexley Council after taking up the mayoral adviser post in May.
I am guilty of a stupid and crass mistake and I have been punished quite correctly for that
Ian Clement, deputy mayor for external relations
Mr Biggs said: "You have to seriously question the judgement of a mayor who was elected on a promise of openness and transparency, yet stands by an aide who has used City Hall as his personal bank account.
"Hard up Londoners will find it hard to agree that Boris's behind-closed-doors investigation and slap on the wrist is a proportionate response to such blatant and consistent abuse."
In a letter to Mr Biggs, the mayor said that the "sanction taken against any member of staff in the organisation, in line with the code of ethics, is confidential to that individual".
Speaking outside City Hall, Mr Clement said: "I have made a mistake and I have accepted responsibility for that and I have been disciplined.
"In addition to that discipline the mayor has made it perfectly clear his disappointment and anger.
"I am guilty of a stupid and crass mistake and I have been punished quite correctly for that and I have taken my punishment and I have apologised for that."
When questioned about Mr Clement's expenses, the mayor said: "There's a difference between what is crass and what is appropriate, what makes me angry and what is actually dishonest.
"He shouldn't have been buying things on a corporate credit card, that is absolutely wrong.
"He did repay them, that was the critical thing for me."
After the personal expenses came to light Mr Clement was forced to hand back the credit card following an internal inquiry, the mayor's office said.
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