Blair is due to give evidence to the inquiry into the war, led by former civil servant John Chilcot, early next year, and the commentator in the Sunday Telegraph said the investigation's focus must now change.

"Mr Blair's game-changing admission gives them a licence to be tougher and more prosecutorial," he wrote, a call echoed by campaigners at Stop the War Coalition, who urged Chilcot's inquiry to recommend legal action against Blair.

Professor Philippe Sands, a leading international lawyer, said he believed Blair's comments had left him open to legal action.

"The fact that the policy was fixed by Tony Blair irrespective of the facts on the ground, and irrespective of the legality, will now expose him more rather than less to legal difficulties," Sands told The Sunday Herald.