Nicola Sturgeon was canvassing in Stirling with Alyn Smith but Ian Blackford may need her help more

An informal pact has emerged to oust the second SNP Westminster leader in as many years by giving ground to the Liberal Democrats.

Senior figures in the Scottish Conservatives and Scottish Labour believe that Craig Harrow, the Liberal Democrat candidate, is on course to topple Ian Blackford in Ross, Skye and Lochaber and have effectively downed tools on campaigning in the constituency.

Mr Blackford has a majority of almost 6,000 but his share of the vote fell by 7.9 per cent in the two years leading up to the 2017 election.

The Tories finished second then, but the seat is considered Lib Dem heartland and was held by Charles Kennedy, the former party leader, for a decade.

He lost it during the SNP surge and