Image caption The review will determine the shape and size of British armed forces for the next generation

The speed of a crucial review of defence needs could put combat operations and UK security at risk, the chair of an MPs' committee has said.

Tory James Arbuthnot said the Defence Select Committee was worried the process was money-driven and not taking time to assess the threats to the UK.

He said it was "potentially detrimental to the defence of the country".

David Cameron said the review would ensure the armed forces can protect the UK's interests at home and abroad.

Speaking during Prime Minister's Question Time, he said it would "properly review how we can make sure that we have forces that are right for this country".

Ministers said in an "ideal world" the process would take longer but there was an urgent need to tackle the deficit.

Asked about the impact of the review - and expected future defence budget cuts - on troop morale, Defence Minister Nick Harvey said Afghanistan remained the UK's top priority and nothing would be done to "cause alarm" to front-line operations.

It is essential that we both deal with operations [in Afghanistan] and the emerging threats that are coming up against us over the coming decades James Arbuthnot, Defence Committee chairman

Shadow defence secretary Bob Ainsworth said it was a mistake to base the structure of the armed forces for the coming decades on a "short-term financial situation".

"[The government] are doing it in haste because it appears they are not prepared to share their thinking with the nation," he said.

The coalition government has said the strategic defence and security review, which began after the election and which all three major parties backed before May, is due to report next month. The last review, in 1998, took more than a year.

The review is designed to look at the UK's role in the world, evolving threats to the country's interests, the nature of the UK's response to such threats and whether the armed forces are equipped to deal with future challenges.

Annual defence spending in the UK currently stands at about £37bn, which is around 2.5% of GDP. Cuts of 10-20% are expected.

The proposals are not yet known but speculation on the cuts has ranged from the scrapping of new aircraft carriers and trimming back Trident to cutting the Army's troop numbers by up to 20,000. Proposals are also said to involve grounding the RAF's entire fleet of more than 70 Tornado jets years earlier than planned.

Defence Secretary Liam Fox has insisted the review will be "comprehensive and coherent" and, despite it taking place against a backdrop of looming cuts in public spending, will be driven by strategic rather than financial considerations.

Analysis The Defence Select Committee's report echoes concerns inside the military and the Ministry of Defence that the strategic defence and security review is being driven as much by the Treasury as by national security. The MoD is being asked to make savings of up to 20%, but the real figure will be higher because the ministry already has a black hole in its budget of £37bn. Defence Secretary Liam Fox insists that by the end of the process the UK will still be able to deal with current and future threats. But the scale of the cuts certainly raises doubts. The UK currently has about 10,000 troops in Afghanistan, but it needs another 50,000 to sustain the operation, bearing in mind that soldiers are replaced every six months and need time for rest and training. If the Army were to lose as many as 20,000 troops, as has been suggested, then that would leave it severely stretched. Military might or saving money?

But analysing its progress to date, the cross-party committee of MPs said the review was being undertaken too quickly and there was a consequent risk of "serious mistakes" being made.

It highlighted what it said was a lack of consultation with the public, which it said was vital for maintaining support for future military operations, and with defence contractors.

Failure to engage with industry meant the UK's ability to deliver future military capabilities on time and on budget - while protecting vital manufacturing skills - was under question.

Mr Arbuthnot told Radio 4's Today programme: "We are worried that this process appears to be money-driven rather than driven by the threats to our country which need to be worked out and assessed in order to work out whether, and the extent to which, we can defend against them.

"We are conducting very important operations in Afghanistan and it is essential that we both deal with those operations and the emerging threats that are coming up against us over the coming decades."

When asked whether the committee believed those operations were at risk, he said: "We do, yes, because there have been constant pressures on the defence budget over the period of our operations in Afghanistan - and concurrent operations that were going on in Iraq - and now we are looking at significant increases in the reductions of spending of defence money."

Mr Arbuthnot said the committee welcomed the secretary of state's statement that it would be a real review rather than just a cost-cutting exercise.

But he added: "We are not yet convinced that the combination of a budgetary straitjacket, the short timescale and the apparent unwillingness by the ministry to think outside existing structures, for example with regard to the more integrated use of reservists, will deliver that end."

The committee also called for clarification of how a next generation Trident, the UK's nuclear programme - which is not included in the review but subject to a separate value-for-money exercise - would be funded.

Top 10 military spenders 2009 USA $661bn

China $100bn (Sipri estimate)

France $64bn

UK $58bn (£37bn)

Russia $53bn

Japan $52bn

Germany $46bn

Saudi Arabia $41bn

India $36bn

Italy $36bn Source: Sipri

The Treasury has said the costs must be met by the Ministry of Defence, which analysts say will put further strain on its resources at a time when the UK is fighting a protracted war in Afghanistan.

Mr Harvey acknowledged the pace of the review was influenced by economic circumstances but said it was a "big picture" exercise that drew on debate that had been going on for some time.

"I can only say in an ideal world we would be taking longer over it but this is not an ideal world.

"It is a world in which we have a £150bn deficit and all the big departments of government have to tackle that as the matter of the most urgent priority."

On Trident, he stressed: "There are big debates to be had about Trident replacement and the size of the budget but they don't impact on the current spending round and what departments will have for the next four years."

'Strategic capability'

Later on Wednesday, MPs used a debate in the Commons on defence spending to warn that cancelling major defence contracts would cost manufacturing jobs.

Conservative Mark Menzies said: "This is about the UK being serious about ever again playing a role as a strategic sovereign capability, about being able to manufacture our own aircraft, to own our own technology, to develop our own high tech skills base and continue to be a world leader in what we do."

Meanwhile, Labour's Mark Hendrick said the government would be wrong to cancel one of the two planned new aircraft carriers for the Royal Navy.

He said that it could result in UK defence companies closing contracts to help build the new US-led Joint Strike Fighter, the aircraft that is set to use the carriers.