Geoff Hoon's three homes: Total cost, next to nothing

He took advantage of the arrangement to rent out his London house – declared as his "main home" to the House of Commons authorities – to a private tenant. At the same time, he claimed more than £70,000 in "second-home allowance" on his constituency home in Derby. This meant that during the Iraq war, and for three years afterwards, the man in charge of British forces had one free residence, another covered by parliamentary expenses, and a third – originally his second home, and therefore initially supported by the taxpayer – funded by rental income.

Mr Hoon, who is now Transport Secretary in Gordon Brown's Cabinet, insisted last night that he had done nothing wrong – and maintained that everything was approved by the Commons authorities. "He took advice from the fees office and all his claims were within the rules," a spokeswoman said.

However, the unusual arrangement returned MPs' generous financial arrangements to the spotlight, after a series of embarrassing revelations over the amount senior politicians have been claiming for their second homes.

Details of Mr Hoon's complicated financial affairs came as David Cameron moved to take advantage of the Government's problems with MPs' allowances, by pledging to give up his second home allowance if he becomes prime minister. The Conservative leader has ruled that he would not ask the taxpayer to fund another property if he moved into Downing Street after the next election – and he would impose the ruling on all ministers who benefited from grace-and-favour homes through their jobs.

Gordon Brown claimed more than £17,000 in allowances towards the cost of staying away from his main home last year, despite the fact that he is provided with accommodation at Downing Street.

At least two more Cabinet ministers – the Home Secretary, Jacqui Smith, and the Foreign Secretary, David Miliband – have declined to live in official homes that come with their jobs, and instead live elsewhere in London and claim thousands for the upkeep of second homes. Ms Smith controversially lists her sister's home in south London as her main residence and claimed more than £22,000 last year for her "second" home in the Midlands where her family lives.

It was also claimed last night that MPs are avoiding stamp duty of more than £10,000 each on second and third homes by claiming it back on their parliamentary expenses.

Meanwhile, Ms Smith insisted that her relationship with her husband remained "strong" despite the embarrassing revelation that the taxpayer had paid for him to watch two pornographic films.

She told The Sunday Telegraph that she was "mortified" when it emerged the pay-per-view movies had been inadvertently submitted as part of her expense claim for running the family home.

But she added: "We've got a strong relationship both personally and professionally – in terms of the work he does in my constituency office. And it's still strong now."