MPs will put pressure on Robin Cook today to release key Foreign Office documents which could shed light on the role of British diplomats in the Sandline affair.

The Labour-controlled Foreign Affairs Select Committee has demanded their disclosure, but is expected to be rebuffed today when it takes evidence from Sir John Kerr, the head of the diplomatic service.

The MPs want to get hold of the telegrams sent by diplomats in Sierra Leone to the Foreign Office in London in order to establish if officials knew about plans by security consultants Sandline International to breach a United Nations arms embargo.

The Foreign Secretary told MPs the documents could not be released because they are ''restricted in circulation'' and could contain information ''embarrassing to Her Majesty's Government and others''.

The Foreign Office's permanent secretary is expected to reject the demands on the grounds of confidentiality and national security. The Government claims that it cannot take any action that might prejudice the ongoing criminal investigation by Customs and Excise.

Today's committee session will attempt to focus attention on the Foreign Office's handling of the affair, which has raised questions about the advice and information passed by officials to Ministers.

The row exploded a week ago when Mr Cook revealed he had not known about the Customs inquiry, or the arms shipment, before he received a letter from Sandline complaining that it was being investigated for activities approved by British officials.

Foreign Office officials refused to comment on reports that a telegram sent last December by the High Commissioner in Sierra Leone, Peter Penfold, warning that Sandline was preparing to break the UN arms embargo, had gone missing.

A spokesman said it was a matter for the Customs investigation into alleged sanctions busting by Sandline and, after that, for the independent inquiry ordered by Mr Cook.

There were noisy exchanges over the affair during Prime Minister's Questions, as Tony Blair brushed aside Opposition attempts to press home the attack.

''I described it as overblown hoo-ha - and that is what it is,'' he declared to Opposition jeers.

Tory leader William Hague concentrated his fire on Mr Cook personally, claiming he was unfit to hold the office of Foreign Secretary. He said the Foreign Office was being run like a ''Dad's Army outfit'' with Mr Cook combining the ''pompousness of Captain Mainwaring, the incompetence of Private Pike, and the calm of Corporal Jones''.

Liberal Democrat leader Paddy Ashdown accused Ministers of adopting the ''Thomas a Beckett defence'' - a reference to the medieval Archbishop murdered after Henry II demanded: ''Who will rid me of this turbulent priest?''

He said the Government had wanted someone else to get rid of the illegal junta in Sierra Leone so it could keep its hands clean while proclaiming an ethical foreign policy.

Mr Blair's press spokesman attacked the media for producing ''some of the most ridiculous coverage I have seen since we have been here''.

He said Mr Blair's praise for Mr Penfold's performance in helping civilians caught up with the Sierra Leone coup was ''entirely consistent with saying it's wrong for people to break the arms embargo''.

The spokesman said Mr Penfold was being questioned under caution by Customs and Excise.

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