An SNP MP has demanded to know why the Scotland Office "requires such an enormous increase in its budget" after receiving an almost 20% rise in the past five years.
Margaret Ferrier claims the increasing devolution of responsibilities from Westminster to Holyrood has left the Scotland Office a "zombie department" and questions the need for extra money.
Figures show the Scotland Office real terms budget, excluding non-voted election expenditure, has increased for three out of five years since 2012/13.
The 2016/17 budget is an 0.4% reduction and it fell by 2.8% in 2013/14 but the remaining increases, including a 14.4% increase in 2015/16, have led to a 19.9% cumulative increase since 2012/13.
At the same time, the SNP said the real terms Scottish Government budget, excluding council tax benefit, landfill tax, stamp duty land tax, Scottish rate of income tax and the £800m capital budget increase pledged by the UK Government in the 2016 Autumn Statement, had led to a cumulative 1.9% decrease over the five years.
Earlier this year it emerged Scotland Office communications expenditure had more than doubled since 2011/12 to £426,223.
Ferrier, who represents Rutherglen and Hamilton West, said: "The Scotland Office has long been a zombie department with next to no responsibilities.
"And with more powers transferring to the Scottish government, as David Mundell so enjoys telling us, it would be interesting to hear his explanation for why his department requires such an enormous increase in its budget.
"We know that the budget for Mundell's army of spin doctors and publicity campaigns to promote the benefits of the union to the people of Scotland has more than doubled.
"Perhaps he needs the extra help in trying to devise a believable reason for why he has U-turned on the single market and why he believes the people of Scotland should suffer Brexit despite not voting for it.
"At a time when households are being told by Tories to tighten their belts, and Scotland's budget which pays for public services is being cut so savagely to the tune of £2.6bn by 2019/20, people are entitled to ask just what David Mundell has done to deserve his budget boost and what is he spending it all on?"
A UK government spokeswoman said: "This year the Scotland Office has ensured the successful passage of the Scotland Act, making the Scottish Parliament one of the most powerful devolved governments in the world.
"It is right we are resourced for the challenges in 2017 as we continue to deliver the remaining powers as well as making sure we get the best deal for Scotland and the whole of the UK as we leave the EU."