LONDON (Reuters) - Britain's spending watchdog, the National Audit Office, has refused to sign off part of the Treasury's 2008/09 accounts due to questions about exposure to bank losses.

It is the first time for almost a decade that the Treasury's accounts have been "qualified", a term which means the auditor is not fully satisfied.

The NAO said it had been unable to sign off the accounts in full since much of the detail of the government's Asset Protection Scheme had yet to be laid before parliament. The Asset Protection Scheme is designed to protect banks from massive losses, encouraging them to free up credit for households and businesses.

The Treasury said the auditor's move was a "technical" and that no concerns had been raised about the estimated cost of the banking measures.

"The NAO has acknowledged that the need to act by introducing the Asset Protection Scheme did not allow time to seek parliamentary approval for the accounting consequences of the scheme, which resulted in a technical qualification of the accounts.

"They have not expressed concern about the figures for the costs of interventions to support financial stability included in the accounts, which are consistent with the range of £20 billion to £50 billion set out in the Budget."

The auditor said the Treasury was one of five government departments to have questions raised over their accounts.

The others are the Ministry of Defence, HM Revenue and Customs, the Department for Work and Pensions and the Home Office.

The NAO is an independent body funded by parliament, rather than the government of the day. However, it has limited powers and its role is largely to draw attention to cases where it feels public money has been misused.