Britain’s social security bill will not be cut to help boost defence spending, the Prime Minister has said.

Andy Burnham criticised Conservative proposals to reduce housing benefit by £4billion, arguing that national security “can’t come at the expense of social security”.

He said that the plan would result in more homeless families and “hundreds of thousands of children” in temporary accommodation.

During Prime Minister’s Questions on Wednesday, Mr Burnham said: “I don’t think myself that taking £4billion out of housing benefit is going to get the right consensus around this issue, because that would create levels of homelessness in this country that we wouldn’t have seen before – hundreds of thousands of children in temporary accommodation.

“We do everything to support our national security, but it can’t come at the expense of social security.

“Having strong national security also depends upon having resilience in our communities.

“This side of the House will not be forced to choose between the two, and we will set out a plan to get to 3.5% (of GDP spent on defence) by 2035 at the spending review.”

Conservative leader Kemi Badenoch replied: “It’s unbelievable that the Prime Minister would say that.

“He’s clearing unwilling. We need to fund out defence, not spend all of our money on welfare.”

Mr Burnham insisted the Government would honour Nato commitments to reach 3.5% by 2035, with a target for 3% funding set out in the spending review.

The Tories set out their plans to fund defence last week, with some £4bn coming from a reformed housing benefit, and a further £3.1bn through reimposing the two-child benefit cap.

Ms Badenoch also accused the Government of being prepared to pay £35bn to hand over sovereignty of the Chagos Islands to Mauritius, but not spend money on troops.

She said: “Last year, defence funding fell in real terms. That is on them.

“To govern is to choose. So why is he choosing to send £35bn to Mauritius when they (Labour) cut the money to train our troops?”

Mr Burnham responded: “I don’t think she’s on strong ground when it comes to defence spending.

“It was 2.5% of GDP when the last Labour government left office. It was 2.3% of GDP when the government she was in left office. It’s now set to be 2.7% in the next year. So that is the reality of the situation.

“It would be better to work across the floor of this House to get a fully and securely funded path to 3.5% of GDP by 2035.”