David Cameron blamed an “inadvertent administrative error” for over-claiming expenses to pay for the mortgage on his second home.

The Conservative leader discovered the £218 over-payment just before his claims were officially published yesterday, according to his spokeswoman.

He also admitted two other overpayments — one on an electricity bill, the other for a staff phone — as he announced that he was repaying a total of £947 to the Commons Fees Office.

George Osborne was the target of a complaint to the office over his claims for the mortgage on his constituency home. The Shadow Chancellor was revealed by The Times as having “flipped” the designation of his official second home after taking out a £450,000 mortgage on the Cheshire property.

John Lyon, the Standards Commissioner, confirmed yesterday that he was considering a complaint that Mr Osborne had claimed interest payments on a debt greater than the cost of the home. The Shadow Chancellor’s spokesman dismissed that allegation, however, insisting that Mr Osborne’s mortgage had included costs of essential repairs to the property.

In a letter to the Fees Office, Mr Cameron said that his mortgage over-payment had been caused as a result of “numerous changes to my monthly repayments” after a fixed-rate deal expired.

He said: “I think the best thing to do when you discover a mistake like this is to deal with it as quickly as possible. I didn’t do this because of any media inquiry, I just thought it was right.”

Another of Mr Cameron’s closest allies, Oliver Letwin, drafted an explanation of his complex mortgage arrangements 24 hours before yesterday’s publication, suggesting he, too, feared allegations of “flipping”.

Mr Letwin, the party’s policy chief, asked if he could lift his expense claim after increasing his home loan by £100,000 in October 2005. He withdrew the claim after it was queried by the Fees Office.

The total repaid by Mr Cameron includes the £680 he had previously promised to repay — for the cost of clearing wisteria and other maintenance work on his constituency home in Oxfordshire. The over-claiming errors may be seen by some as the first real personal embarrassment for the Tory leader from the expenses row.

His claims also include £150 for a lost pager as well as bills for pictures of himself in the House of Commons and for a photograph frame from John Lewis. All the claims were legitimate, his office insisted.

Mr Cameron has come under attack in recent days from Conservative MPs angry at the way he has handled the expenses row. Some privately accuse him of protecting allies while meting out summary justice to those outside his circle.

Other claims by leading Conservatives include £513 by Mr Letwin and more than £1,000 from Chris Grayling, the Shadow Home Secretary, for shredding services.

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