More than 12,000 reservists have served in Iraq since 2003

The Commons public accounts committee said the Ministry of Defence was now "heavily reliant" on reservists - used at "unprecedented levels" since 1997.

But the report says the reserve forces are understaffed and some are not passing basic fitness tests.

Among suggestions was cut-price gym membership to allow volunteers to reach "the necessary levels of fitness".

During the initial "war fighting phase" reservists made up 12% of the total UK force in Iraq, the report said, and more than 12,000 reservists have served in Iraq.

The department has used reserves at unprecedented levels in the last ten years with the reserve forces making an increasingly important contribution to defence Committee's report

There are about 36,000 Volunteer Reserves - largely from the Territorial Army (TA) - and 52,000 Regular Reserves - former services personnel.

The report said: "The department has used reserves at unprecedented levels in the last ten years with the reserve forces making an increasingly important contribution to defence as the regular forces have become more stretched."

It found that the culture had changed so that reservists "now expect and want to serve on operations". Longer serving, older members, were leaving, it said.

Fitness tests

But the TA is 16% under strength while the Royal Auxiliary Air Force had a 36% shortfall in manpower, the report said, although the MoD has said numbers appear to be stabilising.

And people were joining the TA despite failing basic fitness tests, "some commanders in the field in Iraq noted that a number of deployed reservists were not as fit as they needed to be" and some had been evacuated to the UK.

A pilot system to enforce health and fitness standards is due to finish in November, but MPs have demanded interim measures such as a probation period for new recruits.

This, the report said, would enable "applicants time to reach the necessary levels of fitness and negotiating reduced-rate gym membership".

And reservists did not get to train alongside regular soldiers, nor with the equipment used on operations, the report said.

You cannot treat reservists as second-class members of the armed forces while demanding a first-class job from them Edward Leigh Committee chairman

Royal Naval Reservists in particular, rarely went to sea - which did little to prepare them, or to boost morale.

Training often got cancelled at short notice where facilities were shared with regular soldiers, which could damage morale.

And reservists were not "receiving prioritised medical treatment" for injuries sustained on operations - although a new mental health programme had been introduced in November 2006.

The committee's Conservative chairman Edward Leigh said: "The Ministry of Defence cannot have it both ways.

'Poor relations'

"You cannot treat reservists as second-class members of the armed forces while demanding a first-class job from them."

He added that the MoD appeared to be "alarmingly ill-informed" about the fitness of reservists on the front line.

For the Lib Dems, Nick Harvey MP said it was unacceptable to treat reservists as "the army's poor relations".

We set rigorous standards for physical fitness which every reservist deploying on operations is tested against prior to deployment Bob Ainsworth Defence Minister

"It seems nonsensical for the Territorial Army to insist that volunteers take basic fitness tests but then send people who have failed those tests to some of the most dangerous areas in the world," he said.

Defence Minister Bob Ainsworth welcomed the report but said many of the areas of concerns had been addressed in the last year - including welfare, training, recruitment and equipping of volunteers.

He said reservists' contribution to operations was "outstanding" and the MoD would continue to make improvements on areas where it fell short.

He added that they could not afford to lose potential recruits who thought they were not "fit enough" to join the reserves and had to "strike a balance between fitness on entry and an individual's potential - potential that our training can release.