THERESA May has been urged by the Liberal Democrats to accept that there is not enough money going into defence following the intervention of the head of the British Army.

In a speech, General Sir Nick Carter warned that the UK risked falling behind Russia without more investment into defence and claimed that the Army’s ability to respond to threats would be “eroded if we don’t keep up with our adversaries”.

The speech, approved by Gavin Williamson, the Defence Secretary, comes amid fears of more defence cuts.

Raising the issue in the House of Lords, Lord Campbell of Pittenweem, the former leader of the LibDems and now their defence spokesman, suggested it was unprecedented for the serving head of one of the armed services to intervene in a debate on defence spending.

“If the head of the Army and the Secretary of State have now reached the view that there is insufficient investment in defence, is it not high time that the Government did so as well?” asked the Scottish peer.

But Earl Howe, the Defence Minister, pointed out that UK defence spending was rising, not falling. “This year,” he explained, “the budget is £36 billion and it will increase by at least 0.5 per cent above inflation every year of this Parliament to almost £40bn by 2020-21.

“The UK is proud to be the second-largest defence spender in Nato and the fifth-largest in the world. Recent press speculation about changes to the UK’s force structure and cuts to the budget, has been misleading and unhelpful,” he insisted. Lord Howe told peers the National Security Capability Review was about maintaining agility in the country’s security and defence and “staying ahead of the curve” in terms of the resources deployed.

“We must remain agile in a world that is ever changing; it is about ensuring that our defence and security policies and plans are as efficient and effective as possible”, he told the Lords.