CHANCELLOR Alistair Darling is one of four senior Scottish MPs who are claiming tens of thousands of pounds of public money for designated "second homes" despite renting out other flats in London.

The others - John Reid, the former home secretary, Charles Kennedy, formerly the leader of the Liberal Democrats, and government whip Tommy McAvoy - have been accused of claiming the taxpayer-funded perk at the same time as having their own personal property portfolio.

Campaigners have stepped up their calls for the expenses regime at Westminster to be overhauled.

Under the Additional Costs Allowance (ACA), most MPs can claim up to £22,110 a year for staying away from their main home while on parliamentary business.

MPs can use the perk to pay for hotel costs, rent, or mortgage interest - the latter can be used on a home in London or in their constituency.

Darling was criticised last week after it emerged he had charged the taxpayer £70,000 in ACA after designating his £1 million family home as his "second house".

It has now emerged that Darling, Reid, McAvoy and Kennedy are claiming the second home perk while at the same time acting as landlords on properties in the capital.

Darling, who lives in Downing Street rent-free and bills the public for staying in his Edinburgh home, also owns a flat in London with his wife Maggie. His entry in the MP's Register of Members' Interests states the flat is "presently let", but no rental is declared.

He is also entitled to use Dorneywood, a 21-bedroom grace-and-favour mansion in Buckinghamshire reserved for the chancellor.

He also has a family croft on Lewis in the Outer Hebrides.

But despite having access to these five properties, Darling has claimed around £55,000 in the "second homes" subsidy since 2004-05.

Reid has claimed up to £50,000 in the perk over the same three-year period, in spite of the Labour MP being on record as receiving "rental income" from a flat in London since November 2000.

Property records also show that Reid owns a property near Westminster, which he bought for £800,000 in 2001. His business, John Reid Advisory Ltd, has its registered office at the same flat, according to company accounts.

McAvoy, a Labour whip since 1997, also claims the second home allowance while acting as a London landlord at the same time. The Rutherglen and Hamilton West MP has billed the taxpayer for around £64,000 in ACA since 2004.

His entry on the Commons register shows he has received "rental income" on a residential flat in London since November 2002.

Kennedy, who quit as LibDem leader in 2006, is another who doubles up as a second homes claimant and landlord. According to parliamentary figures, the MP charged the taxpayer around £63,000 in ACA between 2004 and 2007. Since at least 2000, Kennedy has also derived rent for a single-bedroomed flat in London.

He told the Sunday Herald that he had previously claimed allowances on the flat when he lived there.

He added: "The ACA is being used towards the cost of family accommodation in London, for which the one-bedroomed flat is not suitable. Therefore it is declared quite separately in the Register of Members' Interests."

None of the MPs declares how much they receive in rent, or who they have as tenants. Around 40 MPs claim the controversial housing perk while also acting as landlords.

Commons rules mean that an MP can buy two houses in London with their ACA, then rent out the first property while charging the taxpayer for mortgage costs on the second.

A spokeswoman for Darling said she had "nothing to add" about the Chancellor's expenses claims.

Rami Okasha, a spokesman for Scottish Labour, said he could not reach Reid or McAvoy for comment.

A spokesman for the Taxpayers' Alliance said: "The ACA is there to help MPs represent their constituents, not to help them build up a property portfolio at taxpayers' expense. It is clear the whole system needs tightening."