Legal advice given to Tony Blair prior to the invasion of Iraq was fundamentally “flawed”, a former senior law lord has said.

Lord Bingham, who stepped down in July, described the action by the UK and US as a “serious violation of international law”.

He said advice by the then-Attorney General Lord Goldsmith failed to acknowledge the lack of hard evidence implicating Iraq’s non-compliance with UN resolutions. Furthermore it neglected to make clear that only the Security Council could authorise further action, Lord Bingham suggested.

But Lord Goldsmith said that he stood by his advice to the then-prime minister.

Lord Bingham’s comments came in a speech on the rule of law at the British Institute of International and Comparative Law. In it he referred to a statement made by the former attorney general in March 2003 as Britain prepared for the invasion.

“This statement was flawed in two fundamental respects,” he said. “It was not plain that Iraq had failed to comply in a manner justifying resort to force and there were no strong factual grounds or hard evidence to show that it had.”

“Hans Blix and his team of weapons inspectors had found no weapons of mass destruction, were making progress and expected to complete their task in a matter of months.”

Lord Bingham added that Lord Goldsmith’s advice passed on the belief that a decision over whether Iraq had not complied with UN resolutions could be made by anyone other than the UN Security Council.

Responding to the criticism, Lord Goldsmith said: “I stand by my advice of March 2003 that it was legal for Britain to take military action in Iraq.

“I would not have given that advice if it were not genuinely my view. Lord Bingham is entitled to his own legal perspective five years after the event, but at the time and since then many nations other than ours took part in the action and did so believing that they were acting lawfully.”