Cherie Blair has regularly courted controversy

The prime minister's wife is said to be penning a book on the history of premiers' wives including details about her own time at Number 10.

Work on the book apparently began at the height of the Cheriegate affair - the row that resulted in an unprecedented apology from Mrs Blair for the embarrassment she caused by buying two flats in Bristol with the help of convicted fraudster Peter Foster.

Mrs Blair has to be careful about how she goes about her business Gerald Howarth

Mrs Blair is believed to be collaborating with Cate Haste, wife of Labour peer Melvyn Bragg, whose books include Nazi Women - a look at the personal relationships which influenced Adolf Hitler - and a sexual history of Britain.

Downing Street has refused to comment on the work, claiming it was a "private matter".

However, the news has provoked concern among MPs.

'Privileged position'

Gerald Howarth, Tory MP for Aldershot, said: "Mrs Blair has to be careful about how she goes about her business.

"Nobody is going to object to her writing a book, but if it turns out to be a political diatribe, she can expect to be criticised," he told the Daily Express.

Liberal Democrat Norman Baker told the Independent: "Once again, it blurs the lines between the political and the private.

"She is in a very privileged position and the book will no doubt be sympathetic to the Labour project."

Mrs Blair is said to have invited Lady Margaret Colville, the 84-year-old wife of the private secretary to Sir Winston Churchill, to talks with her at the family flat in Downing Street.

Seminars

Other wives or husbands of prime ministers have kept much lower profiles than Mrs Blair.

As well as juggling four children and a career, she still finds time to accompany her husband on a good number of overseas trips.

She is also known to chair the odd seminar at Downing Street.

During her fourth pregnancy her busy pace continued until just before the birth of baby Leo - and she was aged 45 at the time.

However, Mrs Blair would not be the first prime minister's wife to become an author.

While John Major was in power, his wife Norma published a biography of Dame Joan Sutherland and a history of Chequers.