Veterans minister Johnny Mercer’s attacks on his Labour electoral rival are “sad and desperate”, Sir Keir Starmer has said.

Mr Mercer, who is standing as the Conservative candidate for the Plymouth Moor View constituency, claimed his Labour opponent Fred Thomas was “bloating” his military service.

The war of words began after a hustings event at which both men appeared on Wednesday.

Mr Mercer questioned whether the Labour candidate had served in combat missions during his time as a Royal Marine, as had been reported by the Guardian newspaper in 2023.

Labour has said Mr Thomas is unable to discuss much of his role in the armed forces because of its “sensitive” nature.

Asked about Mr Mercer’s comments by reporters on the campaign trail in south London, Sir Keir said: “I think this is sad desperation that the veterans minister is attacking another veteran who’s got a proud record of service. It’s desperate.

“It underlines everything I’ve thought for a long time, which is that this Conservative Party now is party first through and through and country second and, in my view, that is the wrong way round, is why we’re in the mess we are in in this country.

“And my Labour Party will always put country first and party second. So it couldn’t be a starker difference between us. But it’s sad and desperate from Johnny Mercer.”

Mr Mercer had outlined his concerns on the X, formerly Twitter, writing: “Nobody who serves in Special Forces Support Group claims they are Special Forces.

“Anyone who has served can say if they were or were not actually in combat – the ‘can’t discuss’ line has been used by Walter Mittys since time began.

“Not a single person has put their hand up today and said they fought alongside Fred. Must have been one of those one-man missions that happen all the time.

“He himself boasted of serving in combat missions. It is strange that he now cannot talk about it.”

Sir Keir Starmer speaks to a group of seated men
Labour Party leader Sir Keir Starmer speaking to the media at a school in Vauxhall, south London (Aaron Chown/PA)

A Labour spokesman told the PA news agency that Mr Thomas is a “decorated ex-Royal Marine” who “served for seven years, rising to the rank of captain”.

He added: “Due to the highly sensitive and recent nature of his role, Thomas remains unable to discuss much of his service.

“His certificate of valediction notes that Thomas gained ‘considerable operational experience relative to the time you have served’.

“It notes Thomas’ ‘command on operations overseas’ which saw him ‘lead personnel … in a range of hostile and challenging environments’.”

Mr Thomas said: “I am proud of having served my country for seven years, including overseas on operations. I remain unable to discuss much of my service, something which Johnny Mercer, as a former defence minister, is keenly aware of.”

The Plymouth Moor View constituency is a target seat for Labour.

Mr Mercer held it with a majority of 12,897 at the 2019 general election.