Thanks for the Tony Blair memoirs? An act of charity – or a gesture of contrition?

Tony Blair, who as prime minister led Britain into wars in Afghanistan and Iraq, announced that he will give all the profits of his upcoming biography to help fund a rehabilitation centre for injured soldiers. The former prime minister's £4m advance, plus all future royalties, will be donated to the Royal British Legion which is building a sports centre for wounded personnel.

It is the single largest donation received by the Legion in its 89 years as a charity for Britain's armed forces. In a short statement announcing the donation, Mr Blair's office said yesterday that the former prime minister was motivated by a desire to honour the "courage and sacrifice" shown by British troops. But the donation received criticism from anti-war activists, some soldiers and a number of families who lost loved ones in Iraq and Afghanistan with them accusing Mr Blair of using his donation to assuage guilt over taking Britain into a highly unpopular war in Iraq.

Other critics also pointed out that none of the profits from the book would go to charities in Afghanistan or Iraq where hundreds of thousands of civilians have been wounded.

The book will be published on 1 September and is one of the most anticipated political memoirs of recent years. It is also an opportunity for Mr Blair to influence the historical debate on his 10-year premiership which came to be dominated by the controversial decision to commit British troops in Iraq.

Since leaving office three years ago, Mr Blair has become a wealthy man with estimated assets of £15m and the ability to command six-figure sums for after-dinner speeches.

The final size of his donation will depend on book sales but it is thought that it will be at least £6m – even though Mr Blair has had to pay back an undisclosed portion of his advance because he chose not to serialise the book.

His office would not confirm whether the Royal British Legion was approached before or after Mr Blair's appearance at the Chilcot Inquiry in January where he said he had "no regrets" in removing Saddam Hussein. "The decision was made a long time ago," a spokesman said. "A number of different charities were suggested and he chose the Royal British Legion."

Chris Simpkins, director general of the Royal British Legion, said the money would be put towards the £12m it needs to build the Battle Back Challenge Centre – a rehabilitation sports complex for wounded soldiers.

"Mr Blair's generosity will help us make a real difference to the lives of hundreds of injured personnel," he said.

A number of groups, however, have criticised the donation, including the Stop the War coalition, which is planning a demonstration at a book-signing event by Mr Blair in central London next month.

"Clearly, Mr Blair feels compelled to donate the profits of his book because he has a guilty conscience", said Lindsey German, convenor of Stop the War. "It would have been better if he hadn't taken us into an illegal war in the first place. Blair lied about the Iraq war, he refused to express any regret at the Chilcot Inquiry and his attempt to save his conscience will be little comfort to those who have lost their loved ones."

Families of soldiers who were killed or wounded in Iraq and Afghanistan also voiced opposition to Mr Blair's donation. Frances Shine's son Trooper Stephen Shine, 24, of the 2nd Royal Tank Regiment, lost a leg in an explosion in Iraq. He went on to learn to ski and has benefited from schemes such as Battle Back. Nevertheless, she described Mr Blair's decision to donate millions from the proceeds as an "insult".

"I just think it is too little, too late," she said. "He should have been a man and got up and apologised to the families for an illegal war. I don't think I would want my son to be helped by Blair's money. He can keep it."

Soldiers writing on the Army Rumour Service webforum had a mixed reaction to Mr Blair's pledge. One user, writing under the name "Victorian_Major" said: "It would be churlish not to welcome this move."

But another soldier, using the name "whitecity" wrote: "He could have offered it to an Iraqi charity for the rehabilitation of Iraqis wounded by UK forces."