The former boss of MI5 has said Iraq was a "distraction" that posed no threat to the UK when Tony Blair took the country to war.
Dame Eliza Manningham-Buller said intelligence suggested the domestic threat could actually increase as a result of the invasion.
The ex-security service chief made the remarks in an interview in which she said she "assumes" there will be bombs attacks in Britain.
"Iraq did not present a threat to the UK," she told the Radio Times about the 2003 war, which was led by the then-American president George W Bush and Mr Blair, who was the British prime minister at the time."The service advised that it was likely to increase the domestic threat and that it was a distraction from the pursuit of al Qaeda.
"I understood the need to focus on Afghanistan. Iraq was a distraction," she said.
"Intelligence isn't complete without the full picture and the full picture is all about doubt. Otherwise, you go the way of George Bush," she continued.Dame Manningham-Buller said it was "for others to decide" whether the war was the right decision.