Boris Johnson faces the loss of a “valued” minister amid reports Johnny Mercer is about to quit the Government.

Veterans minister Mr Mercer is thought to be unhappy about a lack of progress in dealing with former personnel being investigated for killings during the Troubles in Northern Ireland.

He has been heavily involved in the Overseas Operations (Service Personnel and Veterans) Bill, which is going through its final stages in Parliament.

The legislation was developed in response to legal claims made after operations in Iraq and Afghanistan but it does not cover incidents in Northern Ireland.

Johnny Mercer is a valued minister in the Government and we have a good track record on delivering for veterans’ issues

The Prime Minister’s official spokesman acknowledged No 10 was aware of “speculation” around former army officer Mr Mercer’s future but “speculation is what it is at the moment”.

He added: “Johnny Mercer is a valued minister in the Government and we have a good track record on delivering for veterans’ issues.”

The spokesman said he was not aware of any conversations between Mr Mercer and Mr Johnson today.

The Telegraph reported that Mr Mercer has become increasingly frustrated about the lack of progress on the Northern Ireland issue but he is not expected to announce his resignation until the Overseas Operations Bill completes its passage through Parliament.

Lords amendments to the Bill will be considered in the Commons on Wednesday.

Mr Mercer appeared in the House of Commons chamber on Tuesday evening in order to reply on behalf of the Government to the adjournment debate.