The wife of the prime minister will address The Society of the Four Arts in Palm Beach, Florida, on Tuesday.

Sources close to the club suggest that she could be paid $50,000 (£29,000) for the event, entitled “an afternoon with Cherie Booth”, her maiden name. Downing Street refused to comment.

Cherie Blair, who has been accused before of abusing her position to make money, is billed as the “noted British attorney, human rights advocate and the wife of prime minister Tony Blair”.

It is not the first time that Blair has embarked on a lecture tour apparently to raise money. Public records show that the Blairs have mortgage debts of almost £4m, leaving them with repayments of about £16,000 a month. They are looking for a tenant for their London townhouse, which they bought in 2004 with a 95% mortgage of £3.4m.

Her talk to the society is for members only, although it usually puts tickets on sale to the public once members’ requirements are met. Public and press are barred this time.

Last year Cherie Blair earned a reported £100,000 for a six-day charity tour of Australia and New Zealand. One of the charities, which held a gala event with Blair as star speaker, last week issued a public apology after admitting that it did not give enough of the money raised to good causes.

In October 2004 she reportedly earned an estimated £30,000 for lectures in Detroit, West Virginia and Massachusetts, and gave a lecture in Washington last June on the eve of an official visit by her husband to the United States.

Last year the prime minister listed his wife’s speaking tours for the first time in the MPs’ register of interests. He admitted that her lectures included “some discussion” of her life at No 10 but did not disclose how much she earned.

Chris Grayling, the Tory MP who has called on Cherie Blair to donate earnings from speaking tours to charity, called on Downing Street to be more open. “After the rumpus over the charity lecture she gave in Australia, when she was paid more than the charity itself, I had hoped that No 10 had learnt its lesson and realised her commercial lectures were inappropriate,” he said. “It is not just that it potentially undermines the office of the prime minister, but also there is a question mark over whether it is a breach of the ministerial code.”

A society official said last night: “We never discuss the question of any fees we may or may not pay our guest speakers.” But an employee of one of the celebrity booking agencies said: “For big names the society pays $50,000 and sometimes much more than that.”

Before delivering her speech, Mrs Blair is expected to lunch at a private members’ club, Everglades, which has been accused of racism against blacks and Jews in the past.

Her son Nicky, 20, is reported to be accompanying her on the trip.

The Society of the Four Arts, founded in 1936, is one of the oldest “non-profit cultural organisations” in America. Its lecture halls, concert hall, two libraries and beautiful, though hurricane-damaged, gardens run along the Intracoastal Waterway on some of the most valuable land in Florida.

Mrs Blair has told friends she “needs the money” from lectures.

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