BORIS Johnson has downgraded his defence of the Union by failing to appoint a back-up minister at the Scotland Office during his Cabinet reshuffle.

The Prime Minister dismissed Scottish Tory MP David Duguid as a junior minister at the Scotland Office last Friday, but has not replaced him.

Duguid, the MP for Banff and Buchan, was Parliamentary Under Secretary of State, a number two to Scottish Secretary Alister Jack, and also an assistant whip.

Iain Stewart MP, a Scot who represents Milton Keynes, remains as the Under Secretary in the Whitehall department but a third minister has not been appointed.

The National:

Scottish Tory MP David Duguid, pictured above, was sacked as a Scotland Office minister last week.

With Johnson’s reshuffle complete, the move has led to speculation that the post will not be filled or that the Prime Minister had difficulty finding a replacement from the remaining five Scottish Tory MPs.

Douglas Ross is the party’s Scottish leader and David Mundell, no ally of Johnson’s, was previously sacked by Johnson as Scottish Secretary.

Andrew Bowie, formerly a private secretary to Theresa May, and Borders MP John Lamont were overlooked in the reshuffle.

The Prime Minister’s spokesman was unable to provide any clarification but Whitehall insiders expect that there could be another appointment “in due course”.

READ MORE: Jeremy Paxman says he would vote for Scottish independence

Speculation that the post could have been offered to Baroness Ruth Davidson, the former Scottish party leader who now sits in the Lords, has been ruled out.

Davidson, an arch critic of Johnson, discounted herself from taking on any major role while her son, Finn, is an infant.

Mhairi Black the SNP MP, commented on Duguid not being replaced.

She said: "Perhaps the UK government is waking up to the reality that the Scotland Office has become utterly redundant since devolution and is merely a Tory propaganda unit that Scottish taxpayers are having to pay for.

"A report published by the Scottish Affairs Committee made this clear when it questioned the department's usefulness and recommended a review of the existence of the department."