JO Swinson will today present herself as the fresh alternative to be Britain’s Prime Minister as expectation grows that at least one more MP defector will be unveiled at the Liberal Democrat conference in Bournemouth.

With senior colleagues highlighting the “energetic contrast” she will present to voters in relation to the Tories’ Boris Johnson and Labour’s Jeremy Corbyn, the Scottish MP, in her first keynote speech to the party faithful as their leader, will brand the Conservatives and Labour “tired” and “old”; parties which are looking inwards at a time of national crisis.

And she will claim the forces for Remain are “on the verge of stopping” Brexit.

Chuka Umunna, the former Labour MP-turned-Lib Dem, claimed Ms Swinson would be the “big wild card” in the forthcoming election.

“People massively underestimate the impact Jo will have during a General Election campaign,” he said, pointing out how in the polls she had a positive lead over Mr Johnson and Mr Corbyn.

“If that is the impact after a few weeks, just think about the impact in the eye of the storm of an election campaign,” declared the London MP.

In her speech, Ms Swinson will say: “Our country needs us at this precarious time. We do not have 10 or 15 years. We need to seize the opportunity now. Let me be clear: there is no limit to my ambition for our party. And today I am standing here as your candidate for Prime Minister.”

At the core of her keynote address will be what is now the Lib Dems’ flagship policy: to scrap Brexit in a forthcoming General Election campaign.

“The first task is clear: we must stop Brexit. And we are crystal clear: a Liberal Democrat majority government will revoke Article 50 on day one. Because there is no Brexit that will be good for our country,” the Scot will insist.

She will argue that ending Britain’s membership of the EU would “put lives at risk” with the threat to medical supplies and will damage the economy, claiming: “This Brexiteer Government want to pay for their ideology with other people’s jobs.”

Ms Swinson will tell conference that when the General Election comes, she “cannot wait to take on the collective forces of nationalism and populism that will be standing on that debate stage”.

She will denounce Mr Johnson for “silencing critics, purging opponents, ignoring the law,” noting: “For someone who proclaims to hate Socialist dictators, he’s doing a pretty good impression of one.”

She will criticise Mr Corbyn for continuing to pursue Brexit even when the dangers of doing so are clear and obvious.

“Nigel Farage might be Brexit by name but it is very clear that Jeremy Corbyn is Brexit by nature,” she will say.

And the MP for East Dunbartonshire will have a direct message for Scotland, saying: “We are building a movement across the United Kingdom that is on the verge of stopping it. You have a part to play in a growing, strengthening, winning campaign across the UK...

“A big vote for the Liberal Democrats in Scotland at the general election will give us the final push that we need. The energy is with us. Come with us to stop Brexit.”

Party sources told The Herald that a “huge opportunity” was opening up for the Lib Dems north of the border with the right-wing Johnson Government, the departure of Ruth Davidson from the Scottish Tory leadership and the collapse of Corbynite Labour in Scotland.

“We can push through the middle and become the pro-UK, pro-EU alternative to the Nationalists,” insisted one senior insider.

After six MPs defected to the Lib Dems over summer, including the former Conservative minister Sam Gyimah, unveiled on the first day of conference, one senior source pointed to the possibility of another revelation at today's end.

But he stressed people should be “modest in their expectations,” confirming, however, the party had been talking to Heidi Allen, the former Conservative MP-turned-Independent.