Gavin Williamson was shocked at what one source described as “completely awful” headline proposals drawn up by military chiefs

A defence minister has threatened to resign if the military is forced to impose cuts that include reducing the army to below 70,000 soldiers, The Times has learnt.

Tobias Ellwood, veterans minister, has shared with colleagues his “deep discomfort” at a list of cost-saving options faced by the Ministry of Defence.

Gavin Williamson, the new defence secretary, was shocked at what one source described as the “completely awful” headline proposals drawn up by military chiefs.

Mr Williamson, who took charge of the department from Sir Michael Fallon three weeks ago, has signalled that he is ready to take on Philip Hammond, the chancellor, if necessary. “We are beginning to try and push back,” a Whitehall source said.

Other cost-saving options include delaying the upgrade of