The Liberal Democrats could “shake the foundations” of British politics by finishing ahead of not only the Conservatives but also Labour in this month’s European elections, leader Sir Vince Cable has said.

Speaking to The Independent, Sir Vince said the “confusion and disorientation” of the two major parties over Brexit had created conditions where the Lib Dems could outpace both their rivals in a national election for the first time in a century.

After generations of being told a Liberal Democrat vote is “wasted” because of the domination of the big two parties, it is now “abundantly clear” that voters who back European Union membership should consider voting tactically for them on 23 May, he said. “I think there is a recognition that we are clearly the strongest of the three parties on the Remain side and people who think tactically will get behind us,” said the former business secretary.

Citing a tactical voting website set up by campaigner Gina Miller, which favours a Lib Dem vote in all corners of England as the best means of opposing Brexit, he said his message to Remain-backing supporters of other parties was: “Use your vote to maximum effect and vote for us.”

“I’m not predicting it. It will be difficult… But it could happen. That would really shake the foundations.”

Cliffs of Dover lit up in Brexit protest Show all 5 1 /5 Cliffs of Dover lit up in Brexit protest Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this statement by Nigel Farage on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this statement by former Brexit secretary Dominic Raab on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this message to the EU on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this message on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this message on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter

He made clear his ambitions stretch beyond a third-place finish behind Labour and Nigel Farage’s Brexit Party: “What would shake the tree would be if we overtook Labour. That would be a big ask, but it is possible.”

Sir Vince was speaking as a YouGov poll showed the Lib Dems for the first time pulling narrowly ahead of Labour in the European election race, with support of 16 per cent compared to 15 per cent for Jeremy Corbyn’s party, with Conservatives in single figures on 9 per cent trailing in fifth place behind the Greens.

The veteran Twickenham MP said he hoped momentum built up by success in local and European elections will make Lib Dems “key players” in the next general election, with a “big if” over the question of whether Tories or Labour can hold together in their current forms. “They are giving every sign of reaching their sell-by date,” he said. “All kinds of possibilities are opening up.”

Cable and the Lib Dems campaigning for the European parliament elections (Getty) (Getty Images)

Lib Dems had “conversations” with moderate Tories prior to the creation of the Independent Group in February, he said, adding: “If the hard Brexiteers take over … I think we are going to get back to that kind of conversation before long.”

He claimed to have heard rumours that some potential Tory leaders might be open to inviting Mr Farage into the party, something which he said could provoke a “realignment of British politics” by making mainstream Conservatives reconsider their allegiances.

Refusing to name a preferred contender to succeed Ms May, he said: “Even the ones who initially came across as more moderate and reasonable, like Jeremy Hunt, are falling over backwards to appeal to the backwoodsmen, and they have lost all credibility as far as I’m concerned.”

Sir Vince was among a delegation from Remain-backing parties who met Ms May’s effective deputy David Lidington to discuss the Brexit process last week.

He said he had picked up indications in various conversations with the government side that they were privately preparing for the possibility of a Final Say EU referendum.

“When we have been to see people they repeat the mantra that they don’t like the idea, but it emerges that they have been doing a lot of groundwork anticipating it could happen,” he said.

On the Labour side, it was clear from their public comments that senior figures like the shadow Brexit secretary, Sir Keir Starmer, and the deputy leader, Tom Watson, were “trying to get Corbyn into a more unambiguous position” on a people’s vote, he said.

But he added: “I think it’s too late for them.”

Vince Cable spoke to The Independent in his House of Commons office (Andrew Woodcock/Independent)

He said it was “a matter of great regret” that the Lib Dems had been unable to form a combined Remain ticket with pro-EU parties Change UK and the Greens, but said he was hoping to get back into a “collaborative working relationship” with Change UK following the elections, naming interim leader Heidi Allen as “a very easy person to deal with”.

And he rejected the idea that Lib Dems should treat the Euro elections as a “quasi referendum” in which the combined totals for Brexit and Remain parties could settle the question of whether the country still wanted to leave the EU.

“We are treating it as an opportunity to choose MEPs who will hopefully be there for the next five years, and we want as strong a contingent as possible,” he said. “We will fight separately for a referendum when parliament gets down to business again.”

A 30 per cent-plus total for the Brexit Party “would not prove anything”, he said. “We know there is about a third of the electorate who are solid hardline Brexit. We think there is a bigger group on the other side who are solidly committed to Remain and then a smaller, diminishing, group in the middle who don’t know.”

He dismissed Mr Farage’s calls for a “WTO Brexit” – leaving the EU with no deal and falling back on World Trade Organisation rules – as a “complete fraud” and said he was ready to debate the former Ukip leader on live TV to expose his position.

“There is no such thing, the system isn’t working any more,” he said. “The WTO is wonderfully conceived, but it is a very weak, toothless organisation. To see that as an option is grossly dishonest, and that has to be exposed.”

Sir Vince refused to reveal targets for MEPs or vote share in next Thursday’s election, exercising his habitual reserve as he said: “I started off with quite modest objectives to improve on last time, when we had one MEP. I now think we will do better than that.”

Following years in the doldrums as voters punished the party for its participation in coalition with David Cameron, the leader said he detected an upswing in morale on the back of local elections in which they gained more than 700 councillors and 10 authorities.

And looking ahead to the general election, he said that seats which just months ago were beyond Lib Dem ambitions are “now back in play”, citing Leeds North West, which they lost to Labour in 2017, and Chelmsford, where the party won control of the town hall for the first time in 20 years this month.

Despite having announced his intention to step down as leader this month, he indicated he would stay at the helm in the event of an immediate general election prompted by a bloodbath for the Tories at the European polls.

“I’m not going to stay on and on like Margaret Thatcher because we’ve had a burst of positive news,” he said. “But in the unlikely event of a general election before the summer, I will be leading us into it.”