As Labour struggled with outgoings so large that it had to resort to secret loans from millionaires to stay afloat, Mrs Blair made the party pay £275 a day for a month to keep her hair in shape. The invoice from André Suard, her hairdresser, is declared by Labour as an election expense in its annual statement of accounts for 2005 submitted to the Electoral Commission last month.

The Times understands that his invoice describes the services rendered to Labour’s election effort as “hair styling for Cherie Blair”. He charged a daily rate of £275 between April 6 and May 6, the day after her husband won Labour’s historic third term.

The disclosure caused fury last night in Labour’s ranks as the party tried to motivate its demoralised and shrinking membership to fight another difficult round of local elections in which it faces heavy losses. Peter Kilfoyle, a backbench MP and former party official, protested that the bill was twice the sum spent on his own election campaign in Liverpool Walton.

Mr Kilfoyle said: “This is a real problem. We are almost accepting by stealth a First Lady. We don’t have a First Lady in our constitution, whether the Labour Party constitution or the unwritten British constitution; £7,000 could have been spent on political campaigning. We spent about £3,500 on our election [in Liverpool Walton]. It would be a very healthy contribution in many seats.”

A Labour spokesman said last night: “So what? Mrs Blair worked fantastically hard during the election and visited more than 50 constituencies during the campaign and we won the election.”

Disclosure of the bill comes as The Times has learnt that the police investigation into the “cash for peerages” affair is to be widened to cover the issue of whether or not the loans were granted at a commercial rate.

Metropolitan Police officers have been handed paperwork relating to Labour’s loans signed by its millionaire benefactors and party officials, and are to interview the individuals who made the loans shortly.

Mr Suard, of the Michaeljohn salon in Chelsea, often accompanies Mrs Blair on official trips aboard, and was part of her entourage when she and Tony Blair visited Australia, New Zealand and Indonesia last month.

But unless she is travelling as the guest of a charity or other organisation, Mrs Blair pays his fees herself and has frequently complained to friends that she feels it is unfair that she must meet expenses she sees as linked to her role as the Prime Minister’s wife.

During the election campaign, when she reverted to the role of wife of the Labour leader rather than the Prime Minister’s consort, she saw an opportunity to relieve herself of the financial burden, albeit temporarily. Mrs Blair has used the same personal stylist for more than ten years and caused concern when, a month after her husband took office, she flew Mr Suard to Denver for the G7 meeting of world leaders in June 1997, Mr Blair’s first international summit. She was said to have paid the £2,000 cost herself, including flying him economy class to Denver and booking him into the Holiday Inn for four days to tend her hair twice daily.

The disclosure is likely to cause outrage among Labour activists worried about the future of the party after it borrowed £14 million from rich businessmen to stave off a financial crisis before the election.

The row over the loans, which bypassed the Government’s own rules for declaring political donations, caused the most serious “sleaze” allegations of Mr Blair’s time as Prime Minister after it emerged that four of Labour’s benefactors were nominated for peerages.

Labour has been forced to put up for sale its headquarters in Old Queen Street, Westminster, a listed five-storey Georgian townhouse which it bought in 2002 with a £5.5 million mortgage. Party chiefs hope to get £6 million. The £500,000 proceeds would be dwarfed by the demands from several of Labour’s rich backers that their seven-figure loans must be repaid with interest charged at commercial rates.

Ian McCartney, the party chairman, said last year that membership had fallen below 200,000, half that at the height of Mr Blair’s popularity, amid a perception among traditional supporters that Labour has lost touch with them.

Labour spent £17.9 million on its 2005 general election campaign, fair exceeding the £10.9 million bill for the 2001 election. Its biggest bill last year was for advertising, which made up 29 per cent of its spending.

It spent 16 per cent of the total on rallies and campaign events, 15 per cent on direct mail leaflets and 12 per cent each on transport and “overheads and general administration” — a category wide enough to cover the hair styling bills of the leader’s wife.

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