Anthony Seldon has already written one book on the Blair government

Historian Anthony Seldon also wrote the authorised biography of former prime minister John Major.

Governors have given him a term's sabbatical from his post at Brighton College while he works on the book.

He has been asked to complete it in time for publication on the 10th anniversary of Mr Blair's election to the leadership of the Labour Party, in the summer of next year.

Dr Seldon has already written an analysis of the first term of the Labour Government, The Blair Effect, published in 2001.

Brighton College's chairman of governors, Robert Seabrook, said: "Dr Seldon will be in his seventh year as headmaster and this gives him a well-deserved opportunity to recharge his formidable batteries.

"He is totally committed to Brighton College for the foreseeable future and the governors feel that it will be very much to the advantage of the college as a whole that he return after his break with renewed vigour and ideas to build on all he has done."