Liberal Democrats must offer voters an alternative to the left-wing politics of Jeremy Corbyn and the hard Brexit policies espoused by Tory Boris Johnson, a senior party figure has insisted.

Former Scottish party leader Tavish Scott called on the party to fill “the glaring gap in modern politics”.

He warned that if the party could not be relevant “then the world will pass us by”.

He spoke out after the Liberal Democrats’ UK leader, Sir Vince Cable, announced plans to step down after Brexit is “resolved or stopped”.

Voters who are “liberal-minded” will be allowed to sign up for free under plans to bolster membership, he announced.

The party has languished in the polls and struggled electorally since going into government in coalition with the Conservatives in 2010.

Sir Vince said on Friday that he wanted to create a “movement of the moderates” that would bring together voters who loosely identify with the party.

Mr Scott agreed that “party reforms are long overdue”, but in his speech to the Scottish Liberal Democrat conference in Dunfermline, he cautioned to “be careful with anyone voting for our leader”, recalling how Mr Corbyn was elected Labour leader after his party allowed non-members a say.

The Scottish Lib Dem MSP said: “Be sure if we don’t change, if we don’t represent hope, if we are not relevant then the world will pass us by.”

He stressed that “this country needs better than it currently has”, saying that meant there was an “opportunity” for liberals, although he conceded: “We have not set any heather on fire since 2016, despite being the only avowedly pro-European party who should at least get a hearing from 48% of the electorate.

“Tony Blair said yesterday that if the British public are offered a choice of Corbyn versus Boris at the next election they will be looking for something else.

“He is right. And we need to make that alternative us. That is the glaring gap in modern politics.

“This is a time when liberals have been needed by the nation like never before.”

He described the Lib Dems as being “international in outlook” with a “searing sense of social justice and a belief that government must be for the people and not the party”.

He also stressed they were “in favour of bringing our country together, not the divisiveness of English or Scottish nationalism”.