The Scottish Conservatives are in somewhat bullish form at the moment.

The party is talking up its chances in May’s Holyrood elections, suggesting that it could leapfrog Labour to become the second largest MSP group.

But the Tories could face a new challenge to their ability to hold on to their only MP north of the Border in 2020.

And the threat is coming from Downing Street.

David Cameron is determined to push ahead with his plans to cut the number of MPs from 650 to 600.

The Boundary Commission for Scotland will soon begin work that will feed into a process designed to redraw the entire political map of the UK.

Not only will 50 seats overall be cut but the size of constituencies will be equalised, with some notable exceptions ,in an attempt to have roughly the same number of voters in each one.

If, as expected, the shake-up closely follows the results of a similar exercise in 2013 hundreds of constituencies could be affected.

Mr Cameron has reportedly pledged a ‘no Tory left behind’ strategy, and many senior Conservatives believe that overall the policy could give the party an extra 20 seats across the UK at the next general election.

But Tory sources south of the Border admit that the changes could cost the party their sole MP in Scotland, David Mundell, who was received praise from across the political spectrum this week after announcing that he is gay.

The last time the exercise was run Mr Mundell complained that the proposed changes to his constituency in the Borders were a matter of regret.

A lot has changed since then, however, not least that his main challenger is now the SNP.

The Scottish Secretary, known as an effective local campaigner, did manage to hold onto his seat amid the SNP surge in May, but with a much reduced majority of 798.

There could be problems for another “last man standing” as well, Labour's sole MP Ian Murray.

The Edinburgh MP is expected to be affected.

The city lost an MP altogether when the exercise was run a few years ago, before Mr Cameron's plans were halted by his then coalition partners, the Liberal Democrats.

Sources jokingly admit that unlike a few years ago Mr Murray will not be fighting any other Labour colleagues for the chance to fight his seat if it is amalgamated with another.

They also point out that there will be years to campaign on any new boundaries.

But Labour MPs across the UK fear that the entire process could be used by the left-wing of the party to try to trigger a clear out of Blairites.

Overall, however, the main party to suffer in Scotland could be the SNP.

The party famously took 56 of the 59 Scottish seat at Westminster in May.

But under Mr Cameron's plans Scotland can expect to lose a total of around seven seats, bringing the constituency total to around 52.

Watch out perhaps for some who make the switch to standing in the next Holyrood elections, instead of going head to head with party colleagues.