The firm responsible for signing off the books of collapsed tour operator XL Leisure is facing an investigation.

BDO Stoy Hayward’s conduct as auditor of XL and its subsidiaries in the year to October 2007 will be investigated by the Accountancy and Actuarial Discipline Board (AADB). It follows a referral by the Institute of Chartered Accountants of England and Wales.

XL was the UK’s third largest tour operator but fell into administration last month, leaving tens of thousands of holidaymakers stranded.

An investigation does not always mean that an allegation has been made or there is any evidence of misconduct, the AADB said.

But if the board’s probe does uncover wrongdoing, sanctions available include reprimands, unlimited fines or even taking away a company’s professional licence to operate.

A BDO spokesman said: “The administrators for XL have previously confirmed that XL entered into administration having suffered as a result of unpredictable fuel prices, the economic downturn, and were unable to obtain further funding.

“It would be inappropriate to make any comments during an investigation but we will of course co-operate in any way we can with the AADB.”

XL’s collapse came after talks with its Icelandic backer, investment bank Straumur, over the refinancing of the firm’s £143 million debts finally foundered last month.

Chief executive Phil Wyatt blamed record oil prices and a worsening economy for the firm’s woes.

The tour operator called in Kroll as administrators in the early hours of September 12 despite being open for bookings only hours earlier.

The move threw the future travel plans of an estimated 200,000 people into jeopardy and left about 50,000 XL package holidaymakers and an additional 10,000 XL Airline passengers overseas without means of returning to the UK.

Mr Wyatt said he was “devastated” at the company’s collapse and apologised to his customers and employees.

An ICAEW spokesman said the referral of BDO to the board had been made “in the public interest”.