SCOTTISH Tory leader Ruth Davidson has lost a key aide ahead of the 2016 elections.

Chief of staff Lindsay McCallum unexpectedly quit amid a rumoured rift with her boss.

The 29-year-old, considered a future party high-flier, had been in post less than a year.

Her duties included giving Davidson strategic advice, writing briefings, and liaising with UK cabinet ministers, as well as managing Davidson’s diary.

It is understood she left last month.

After a dry run at the general election, when she stood in the Ross, Skye and Lochaber seat, McCallum had been expected to run for Holyrood next May on the Highlands & Islands list.

However, faced with the prospect of dedicating her 30s to life as an opposition MSP, she decided not to stand, ending a key reason for her to remain chief of staff.

McCallum, who comes from a farming family in the Black Isle, where her mother is an independent Highland councillor, has now returned to London, where she spent three years in public affairs before taking the Scottish Tory job in August last year.

“I heard there had been a furious bust-up with Ruth,” said one Tory MSP.

The loss of her chief of staff has added to Davidson’s recent problems as Tory leader.

Despite high hopes, the Scottish Tories failed to make progress at the election, holding on to their single seat, as their vote share fell from 16.7 to 14.9 per cent.

The Tories’ vote share in England was 41 per cent, and 36.9 per cent UK-wide.

Davidson, a Glasgow list MSP since 2011, has also been accused of “carpet-bagging” after announcing she would try to become a Lothian MSP next May.

Glasgow has one Tory MSP, whereas Lothian has two, increasing her chances of election.

An SNP spokesman said: “First Ruth Davidson gives up on Glasgow – with the prospect of the Tories failing to win any seats there next May – and now her chief of staff quits as a candidate.

“It’s no surprise that even members of their own party are now running away from the Tories ahead of the Scottish election next year.

“The truth is that the Tories have absolutely nothing to offer Scotland other than austerity and a narrow, negative agenda which will once again be roundly rejected at the ballot box in May.”

A LibDem source added: “It seems even the Tories are now refusing to buy Tory spin on their election prospects. After decades of calling for one last push they should start listening to the public and scrap their right-wing illiberal agenda."

McCallum said her decision to go had been a “personal choice”.

She said: “I wish Ruth well. I hope that the party increases its MSPs next year. I think they have a good opportunity and Ruth is a good leader.”

A Tory spokesman said the departure had been “amicable”, adding: “There has been a restructuring of the office and as part of that Lindsay is no longer employed.”