The Nationalists had around 118,200 registered members as of January this year, with the Tories claiming 124,000. But the long-term decline in Conservative membership numbers suggests it will not be long before they are outstripped by Nicola Sturgeon’s party.
The figures were published by the House of Commons library and are based on information shared by the parties themselves.
Labour remains comfortably the largest party UK-wide, with around 552,000 members, while the Liberal Democrats are recorded as having around 100,500 registered supporters.
The decline in Tory membership has been a subject of debate among senior figures for several years. In 1970, the party could claim as much as three per cent of the total UK electorate were card-carrying members.
John Strafford, of the Campaign for Conservative Democracy, told the BBC in January he had heard from local party sources that the membership could be as low as 70,000.
He added that more than half of local associations had fewer than 100 members - and he warned that if nothing was done to make members feel more involved “Labour will wipe the floor with us at the next general election”.
The House of Commons Library report marked the first time the Conservatives have provided official statistics since 2013, when the number was 134,000.
Former party chairman Grant Shapps said David Cameron had “taken some convincing” to release the figures at the end of 2013.
The SNP’s own membership figures have fallen slightly since hitting a peak of 120,000 in 2016.
Derek Mackay MSP, the SNP’s business convener, told The Scotsman: “It is striking that the SNP has twice as many members as all the other UK parties’ combined by electorate.
“The Tories dwindling numbers means that the SNP now have as many members in Scotland as they do across the whole UK.
“The SNP’s election success is fuelled and guided by our grassroots members from across Scotland.”