The complaint to the Parliamentary Standards Commissioner came from the chairman of the Labour Party in Mr Osborne's Tatton constituency, Laurie Burton.

In a letter to Mr Burton confirming that he will investigate the complaint, John Lyon said: "In essence, your complaint is that between 2001 and 2003 Mr Osborne wrongly identified his main home for the purposes of his claims against the Additional Costs Allowance, and that from 2003 Mr Osborne claimed for mortgage payments that were not necessarily incurred contrary to the rules of the house."

Mr Lyon said he would write to Mr Osborne and ask for his comments.

Mr Burton alleges Mr Osborne took out a mortgage of nearly £5,000 more than the reported price of his house and claimed Commons allowances to cover interest payments on the whole debt, rather than just the cost of buying the house.

Mr Osborne's office says he never changed the designation of his second home for personal gain and that the complaint was a political one.

"George is relaxed about it and has always been very open in answering questions about his expenses," they said in a statement.

But Mr Burton told Sky News he had not made the complaint on a party political basis.

"I'm doing it because I'm an ordinary man of the public who shares the outrage and disgust that people have throughout the country.

"My complaint is not based on the Green Book rules that other people have complained about, my complaint is based on the code of conduct for members of parliament which says that at all times they should conduct themselves in a manner that will maintain and strengthen the public's trust and confidence in the integrity of Parliament."

The Commissioner said he would not launch an inquiry into Mr Burton's other complaint - that the shadow chancellor had "flipped" his second home and avoided paying capital gains tax.

"This is a matter for HMRC (HM Revenue and Customs)", he told him.

The Commissioner's office also said today that he would not be investigating a complaint about Alistair Darling.

One of the Chancellor's constituents was understood to have lodged a complaint that
he "flipped" second home designations four times in four years to maximise expenses.