A British Army officer who won praise for a rousing speech to troops in Iraq has accused the US and UK of failing to plan for after the war.
Col Tim Collins praised the work of UK troops in a difficult situation
Colonel Tim Collins, who has now left the Army, said they should have given more thought to what would happen after Saddam Hussein was deposed.
But he told the BBC he felt it was right to go to war in Iraq and praised the good work of British forces there.
His criticism of planning echoes the findings of a new parliamentary report.
The parliamentary Public Accounts Committee says planning for the post-war period in Iraq was not well thought out, leaving British troops with much to do.
Col Collins told BBC Radio 4's Today programme that in hindsight he had questioned the coalition's motivation for attacking Iraq when preparations for the aftermath were not made.
"There was very little preparation or thought for what would follow on after the invasion itself," he said.
"Nature abhors a vacuum and so do politics. If you knock something down you must be prepared to put something in its place or live with the consequences."
He said the evidence pointed towards the invasion being a "cynical war" inevitable to vent anger on Saddam Hussein's regime, with no regard to the consequences for Iraqis.
"In which case it's a form of common assault," he said.
The BBC's defence correspondent Paul Adams said Col Collins sounded disillusioned.
The officer was cleared by a military investigation over alleged war crimes a year ago and won a libel case against two newspapers who reported false claims against him.
Col Collins' comments came as Kofi Annan told the BBC the US-led invasion of Iraq was an illegal act that had contravened the UN charter.
He said the decision should have been made by the UN Security Council and warned that Iraq's elections could be in jeopardy "if the security conditions continue as they are now".
Liberal Democrat foreign affairs spokesman Sir Menzies Campbell said Mr Annan's comments would be a blow to Prime Minister Tony Blair.
"The Secretary General has seriously undermined British government policy," he said.
"An illegal war has been followed by damaging consequences over which the British and America have no control.
"Every time the prime minister tries to move on from Iraq, he is knocked back."
The pressure group Stop the War Coalition said Mr Annan had confirmed what many people had believed - that there was no legal basis for the war in Iraq.
The UK government defended its decision to go to war, citing the view of the Attorney-General, Lord Goldsmith QC, that it was legal.
A UK foreign office spokeswoman added there was a full commitment to holding elections in January.