Sir Michael Wood, who was the senior legal adviser at the Foreign Office, told the Iraq Inquiry he disagreed with the advice of the Attorney General Lord Goldsmith that military intervention was lawful.

“I considered that the use of force against Iraq in March 2003 was contrary to international law,” he said in a written statement.

“In my opinion, that use of force had not been authorised by the (United Nations) Security Coun­cil, and had no other basis in international law.”

Sir Michael had warned ministers of the danger of going to war without specific authorisation from the United Nations.

Declassified documents show that Sir Michael warned three months before the invasion that it was not certain if military action would be legal.

In a letter to the office of then attorney general Lord Goldsmith, dated December 9, 2002, he said that a “first view” of UN Security Council resolution 1441 – requiring Iraq to give up its supposed weapons of mass destruction – passed the previous month, did not authorise the use of force.

Sir Michael went on to say that a “second view” could be taken that the resolution did offer a “conditional authorisation” for military action. But he warned that there were “possible difficulties” with this argument.

Sir Michael said he did not agree with Lord Goldsmith’s statement on the eve of the invasion that Security Resolution 1441 together with earlier resolutions dating back to the 1991 Gulf War, provided sufficient authorisation.

He also rejected Lord Goldsmith’s earlier view that 1441 was capable of reviving the earlier 1991 authorisations without the need for a further res­ol­ution of the Security Council.

However, declassified documents released by the inquiry show that, in December 2002, he wrote to Lord Goldsmith’s office suggesting it was possible to argue that 1441 did provide the authorisation for military action.

In his letter, Sir Michael said his “second view” was that 1441 did contain “a conditional authorisation” to use force if Iraq failed to comply with its provisions and there was then a further discussion in the Security Council.