The decision to cut Territorial Army training was "profoundly wrong" and could have serious long-term consequences, the chairman of the Commons Defence Select Committee James Arbuthnot warned today.
Defence Secretary Bob Ainsworth came under sustained attack in the Commons over the decision to cut costs to fund operations in Afghanistan.
Mr Ainsworth insisted that no soldier would be sent to Afghanistan without the proper level of training.
He told MPs: "Despite the continued real terms increases, pressures on the defence budget are well documented."
Spending on Afghanistan had risen from £700 million in 2006 to more than £3 billion this year.
"We are adjusting the core defence budget itself to reprioritise towards Afghanistan.
"This means some tough choices. For example, we have cancelled some Territorial Army training that is not related to Afghanistan.
"No individual deploying to Afghanistan does so without the required training. No TA soldier will be deployed on operations unless the Army is satisfied that he is properly trained and properly prepared.
"Those deploying over the next year will continue to be paid for the training that they do as well as the deployment.
"That's what making Afghanistan the main effort means, and I make no apology for moving resources in that direction.
"That means the pain has to be taken elsewhere."
But critics warned that the plan to cut frequent training for volunteers would lead many simply to drift away from the TA, damaging its ability to supply additional troops in future.
Mr Arbuthnot agreed about the need to prioritise Afghanistan within the defence budget.
However, he said: "I think there are two decisions which this Government has taken which are profoundly wrong.
"The first one is to reduce spending on research and development.
"The second one is to do this to the reserves. It is profoundly wrong and it will have long-term consequences for the Armed Forces."
Mr Ainsworth said: "We have got to try to be mindful of permanent damage to our reserves and we have got to be mindful of protecting our research and development.
"We can't completely sell tomorrow in order to pay for today.
"But today is the pressing need, Afghanistan has to be the main effort."
Prime Minister Gordon Brown and Tory leader David Cameron clashed over the TA cutbacks at question time yesterday.
Mr Cameron claimed a TA officer due to go to Afghanistan next year had been told he would only be paid for half his training days before deployment.
"This is totally unacceptable," Mr Cameron said.