The US Justice Department is seeking to question Baroness Thatcher as part of a high-level inquiry into allegations of a "flights-for-favours" corruption scandal at Congress.

Officials have asked the Metropolitan Police to question the former Tory Prime Minister over a meeting she held with leading Republican Tom DeLay in the UK in 2000.

The request, revealed in a leaked Home Office document, forms part of a probe into allegations that congressmen received free foreign holidays from lobby groups in return for influencing legislation.

A spokesman for Lady Thatcher today confirmed that police had contacted her office in order to "clarify" details of a meeting with Mr DeLay in Britain in May 2000

The spokesman said that the substance of the questions was "merely factual", adding: "There was no indication at all that there was anything at all other than that."

He described Mr DeLay's visit as a "courtesy call", typical of those paid by visiting Republicans. He said that Lady Thatcher had not received any payment for the meeting.

However, details of the confidential inquiry, revealed in a leaked Whitehall document published in the Daily Mirror today, could cause embarrassment among delegates meeting for the Tory conference in Blackpool today, where Lady Thatcher's legacy still looms large.

All of the candidates competing to become the next Conservative leader either worked in her Government or have paid tribute to her leadership style.

The leaked document says that the US probe centres on the activities of Jack Abramoff, a film producer and high-profile lobbyist who has raised thousands of dollars for the Republicans.

It says: "US officials are investigating whether Abramoff was involved in obtaining legislative assistance from public officials in exchange for arranging and underwriting trips to the UK.

"One visit to the UK involved a meeting with Mrs Margaret Thatcher, and her evidence is sought about that meeting and her involvement in the alleged deception and violation of US criminal laws."

It added: "It is alleged that Abramoff arranged for his clients to pay for the trips to the UK on the basis that Congressman DeLay would support favourable legislation if they paid for the trip".

According to the Mirror, the holiday involved playing golf at St Andrews, theatre trips in London and luxury hotel accommodation, as well as dinner with unnamed members of the Scottish Parliament. Those contacts are also being investigated.

The document - marked "Secret" - acknowledged that the US request for information relating to Lady Thatcher was highly sensitive.

"There would be considerable interest in this case if it were to become public knowledge," it noted.

"We have been asked by the US to keep this request ‘sealed’, which we take to mean as confidential as possible. This has been relayed to the Metropolitan Police.

"The Metropolitan Police have been asked to handle these inquiries sensitively given the nature of the individual concerned and the background to the request."

Mr DeLay - a close ally of President Bush - stepped down temporarily as the Republican leader in the House of Representatives last week to fight an unrelated corruption charge.

A Texas grand jury has charged the man nicknamed The Hammer, and two political associates, of converting $190,000 (£110,000) in corporate money into individual contributions to avoid campaign finance restrictions. He has described the charge as a "partisan vendetta" brought by political opponents.

The Home Office refused to discuss the issue. A spokesman said: "We can neither confirm nor deny the receipt or transmission of requests for legal assistance".

It is the second time this year that the Thatcher family has found itself unwittingly drawn into legal investigations.

In January, Lady Thatcher's son Mark, 51, admitted unknowingly helping a plot stage a coup in the west African country of Equatorial Guinea. As part of his plea bargain, he paid a three million rand fine ($A663,513) and was given a four-year suspended prison sentence.

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