Labour peer Admiral Lord West of Spithead admitted to prior knowledge of the invasion

A former head of the Royal Navy has revealed he was told Britain would be invading Iraq alongside the US months before the decision was announced, MPs have heard.

In March 2003, as part of a US-led coalition, British forces invaded Iraq under a cloud of political controversy about the legality of military action and amid intense public opposition to the conflict.

Labour peer Admiral Lord West of Spithead made the revelation as he gave evidence before the public administration and constitutional affairs committee on Tuesday, as it examined the role of parliament in the authorisation of the use of military force.

He told MPs: 'I was told as commander-in-chief (fleet) in June, after Camp David meeting, that we would be invading Iraq with America in the beginning of the following year.'

Lord West said he issued a message to the fleet and the Royal Marines to be 'ready for war in the Northern Gulf by December 31', and sent a mine counter measures force fleet to the region.

Promoted to First Sea Lord at the end of August 2002, he said at the Ministry of Defence he was 'amazed to find' people were 'walking back' and saying they were not sure if it was going to happen.

He was giving evidence before the public administration and constitutional affairs committee on Tuesday

'It was quite clear the Government were thinking we have to get Parliament and others on side,' he added.

'But what was interesting was that as it developed, there was all this stuff on weapons of mass destruction and everything, and it did seem to me that people were looking for a casus belli that they could discuss in Parliament.'

Lord West highlighted how 'from then on' it has been assumed Parliament would be consulted before the use of military force, adding how that before the Iraq War that 'hadn't been the case'.

In a now infamous claim, then prime minister Tony Blair told MPs Saddam Hussein was developing weapons of mass destruction, and later said intelligence showed the Iraqi tyrant could deploy chemical and biological weapons within 45 minutes.

At the time, parliament backed Mr Blair's call for war, giving the go-ahead for military action for a conflict that was waged for six years and cost 179 British lives.

In light of the apparent convention set in 2003 to consult Parliament on decisions to authorise military force and asked what role the house should have in this, Lord West said he is 'not at all sure' it is the best thing - before a decision is made to deploy a military force - that it is debated by MPs.

Lord West said he issued a message to the fleet and the Royal Marines (pictured during the invasion) to be 'ready for war in the Northern Gulf by December 31'

'I think there are lots of circumstances where that is a real problem if that happens,' he said. 'I think the debate itself can bring uncertainty in the minds in some of the military.

'We have now got this hybrid warfare, it is clearly not appropriate, I don't believe, for nuclear response... The whole issue of cyber where speed is very much of the essence and yet a really major impact can be caused.'

He added that there are a 'whole raft of issues that make it not necessarily the best thing to happen'.

Former head of the RAF, Air Chief Marshal Sir Glenn Torpy, who also appeared before the committee, said by 'having an open and transparent debate', it hands 'a degree of initiative to your potential adversary'.

He said it also exposes the thinking as well as weaknesses, adding that most adversaries are not constrained by normal behaviour or the boundaries of a transparent and free press, like Western democracies.

'We do need to be very careful about that debate leading to us being at a greater disadvantage than we would already be at,' he added.