Sir Kevin Tebbit gives evidence at the Iraq inquiry guardian.co.uk

The US believed that Britain would take an active part in the Iraq war even if there were no attempts to solve the crisis through the UN, the inquiry into the conflict heard today.

During the first evidence so far from senior military and defence ministry figures, Admiral Lord Boyce, the chief of the defence staff from 2001 to 2003, told the inquiry panel that US generals and America's then-defence secretary, Donald Rumsfeld, seemingly refused to countenance the possibility that Britain would not commit troops.

"No matter how many times you said to senior American officers, and indeed Mr Rumsfeld, that we were not committing our forces until we had been through the proper UN process, and had been through parliament as well, there was a complete reluctance to believe that," Boyce told the panel, chaired by former senior civil servant Sir John Chilcot.

"It was a case of: 'Yeah, I know you've got to say that, but come the day you'll be there.' [That] was the attitude."

Boyce also said that he and other top British military officers found it "very frustrating" that they could not carry out logistical plans for an apparently imminent war because the government feared such preparations would make the public assume a conflict was inevitable.

Boyce said he had not been permitted to make purchases or carry out other practical planning for deployment to Iraq before November 2002, just four months before British troops joined the invasion.

The then-defence secretary, Geoff Hoon, had made this decision as he did not wish news of such concrete planning to leak out while the government was still officially committed to solving the dispute via the United Nations.

Boyce said: "It was very frustrating. I was not allowed to do that. In other words, having refined our theoretical strategic planning, I could not take the next step, which was to implement it and to start doing the necessary purchasing and bringing things forward, getting people in the right sort of place."

In the meantime, Boyce added, all he could carry out was "high-level planning".

The delays meant that one key army brigade was not fully ready for deployment until a day before the invasion started, Boyce confirmed.

Sir Roderic Lyne, one of the five members of the inquiry team, asked him: "I understand that 7 Brigade did not reach full operating capability until 19 March?"

Boyce replied: "So far as the division is concerned, the army division, you're right, they didn't reach full operational capability until March."

Separately, Boyce condemned both Rumsfeld and the UK's then-international development secretary, Clare Short, for what he said were failures in properly planning for the aftermath of the invasion.

Boyce said he was "always extremely concerned about the anorexic nature of the American contribution".

He explained: "The Americans at that particular stage were very much: 'We're going to do the war-fighting, not the peacekeeping.'"

Combined with Rumsfeld's desire to minimise the number of ground troops, this meant "we were desperately under-resourced so far as those forces going towards Baghdad were concerned", he added.

Asked about cooperation between various arms of government, Boyce said: "I thought Dfid [the Department for International Development] were particularly uncooperative, particularly as led by Clare Short. We had people on the ground who were excellent operators from Dfid who were told to sit in a tent and not do anything."

Also giving evidence this morning was Sir Kevin Tebbit, who as permanent secretary at the Ministry of Defence from 1998 to 2005 was the ministry's top civil servant at the time of the invasion.

Asked about funding for the military operation, Tebbit said that while there was not enough money for the MoD as a whole, Gordon Brown, then still the chancellor, did provide sufficient funds for the war.

"At no stage did the chancellor of the exchequer withhold the funds [needed to carry out the operation]," he said. "The problem was a more basic one about the defence budget as a whole. It was just that the defence budget was too small."

Tebbit – who labelled the accusation that the war was waged for oil "completely untrue" – said Britain's generals had never actively sought a role in Iraq, telling the panel: "At no stage, frankly, did I feel that there was an effort by the military establishment to drive the agenda. Whether that was the case in the United States, I cannot say."

But he noted that it was recognised that, in taking part in the invasion, the UK would have far more of a say over what happened in Iraq, a lesson learned from the first Iraq conflict in 1991.

"Unless and until one had boots on the ground, one did not have serious influence on America," he said.