British Army could be cut to just 50,000 over next four years, report warns.

Britain’s military appears once again in line for massive culls after the next general election because of the continuing austerity drive and a lack of commitment by any of the major parties to protect defence spending, Rusi said.

Downing Street has been forced to deny that David Cameron and George Osborne, the Chancellor, are at “loggerheads” over whether to maintain the Nato target of committing two per cent of the nation's finances to defence.

Regular Army soldiers are already being reduced from 102,000 to 82,000 and a new defence review under the next government could see numbers cut again by around 40 per cent, Rusi warned. It would mean the smallest Army since the 1770s, when Britain lost the American colonies.

The report comes ahead a crucial debate in the House of Commons on Thursday when Tory MPs are expected to push for a vote to force the Prime Minister Cameron into a commitment on defence spending. Tensions over the £36 billion (€50 billion) defence budget are high at a time relations with Vladimir Putin’s Russia are strained and the threat from Isil in Iraq and Syria is growing.