LONDON (AFP) - Some 27 MPs are being investigated by tax officials amid revelations over their expense claims, officials said on Saturday.

HM Revenue & Customs confirmed a report in the Daily Telegraph charting a new twist in the long-running scandal which has led to a wave of resignations and raised questions about politicians' probity.

The probes will look at whether MPs broke tax laws in making expense claims. They are only allowed to avoid tax on them if they are "wholly, necessarily and exclusively" related to parliamentary duties.

"Inquiries are an integral part of HMRC's work ensuring everyone pays the right tax," a spokeswoman said.

"An inquiry does not necessarily mean that there is a problem. Most inquiries are closed quickly."

Mike Warburton, a tax partner at the accountants Grant Thornton, told the Telegraph: "The rules are clear and MPs will struggle to argue that claims like horse manure for their gardens are essential."

MPs returned to Westminster after a three-month summer recess this week to find that the expenses scandal, which the Telegraph first highlighted in May, had flared up again.

MPs have spent taxpayers' money on everything from a duck island to gardening, triggering resignations including that of then House of Commons speaker Michael Martin.

Prime Minister Gordon Brown, whose government has been shaken by the row, said on Monday he would pay back over 12,000 pounds in gardening and cleaning expenses.

Both he and David Cameron, leader of the Conservatives, have taken a firm line and warned their MPs to pay back disputed claims or risk their jobs.