A Sussex MP is using taxpayers money to keep a home in London despite owning a second property in the same street.

Francis Maude, the MP for Horsham and a member of the Conservative Shadow Cabinet, said he was totally confident he was following the rules in claiming more than £23,000 in Parliamentary allowances to cover the mortgage on a £345,000 luxury flat in Lambeth, South London, while renting out his £500,000 house a minute's walk away.

Mr Maude, who also owns a £750,000 farmhouse near his West Sussex constituency, increased his claim under the controversial additional cost allowance (ACA), which is designed to enable MPs to stay in London during the week to carry out their Parliamentary duties, from £5,519 a year in 2006, when he bought the flat in which he now lives, to £23,083 in 2007/08.

The MP insisted his only expense claims were for property used for his work as an MP, as permitted under the rules.

However, Lewes MP Norman Baker suggested the behaviour of some MPs in claiming cash for expenditure that was not strictly necessary appeared unethical.

The Lib Dem MP said: "MPs have been encouraged to use a second home allowance to gain economic advantage and play it in the way most favourable to them, which seems to me unethical."

The details of Mr Maude's property portfolio, revealed in a Channel 4 documentary The Westminster Gravy Train, come after a series of claims that senior politicians are abusing the expenses system.

Mr Maude said he had been able to pay off the mortgage on his house while outside Parliament, between 1992 and 1997, before he was elected MP for Horsham, and he was using his ACA claims to pay the interest on the mortgage on his flat.

He said: "We bought outright the house that is now rented and spent substantial sums of our own renovating it.

"When we decided to move to a flat in London it made sense to rent out the house rather than sell it.

"We had paid off the mortgage on our then London property before I was reelected in 1997, from money I had earned while I was out of Parliament.

"I am totally confident that I have acted within the letter and the spirit of the rules in only claiming for a property that I use for my work as an MP."