The letter sent by email on October 31, less than a fortnight after Dennis Hutchings had died and prior to the funeral, suggests that Mr Wallace used it to besmirch Mr Mercer.

Mr Mercer was not mentioned by name, but there is little or no chance he could be talking about anybody else.

A former captain in the Army, Mr Mercer had resigned as veterans’ minister over the Government’s failure to bring in legislation to protect troops from prosecution over historic fatalities in Northern Ireland.

The Conservative MP for Plymouth Moor View, where Dennis Hutchings’s funeral was held, has been highly critical of Boris Johnson and his administration including the Ministry of Defence.

Mr Mercer, who was passed the letter, said it was deeply upsetting that the Defence Secretary had seemingly questioned his motives.

He said: “Ben Wallace served a considerably long time ago as a soldier, for a very short period, with exceptionally limited operational experiences. But even he would know that to suggest another soldier is supporting a veterans family for ‘attention’ is simply a line you do not cross.

“I’m unsurprised. He is one of the chief operators of saying one thing in private and quite another in public.”