Liberal Democrat leader Sir Vince Cable has announced plans to step down after Brexit is "resolved or stopped".

The Twickenham MP said reports of his imminent departure were "very wide of the mark" and insisted he would stay on to steer the party through any Brexit-related turmoil, including any possible general election.

However, in a London speech the 75-year-old said the time would be right for a leadership election after that under new rules he unveiled to widen participation in the party.

Sir Vince also made a naked pitch to disaffected Labour and Conservative MPs and members unhappy at the direction their parties are moving to join the Lib Dems, saying it was better to join an existing centrist party than to start a new one.

He told the audience at the Liberal Club he had already made it clear he did not want to follow in the footsteps of Liberal prime minister William Gladstone, who served into his 80s - or follow octogenarian leader Robert Mugabe.

Sir Vince said: "Reports I have read of my imminent departure are very wide of the mark.

"Now is not the time for an internal election, there is serious work for me and the party to do.

"Once Brexit is resolved or stopped, that will be the time to conduct a leadership election under the new rules."

Voters who are "liberal-minded" will be allowed to sign up for free under plans to bolster membership, the former Cabinet minister announced.

The Lib Dems have languished in the polls and struggled electorally since going into government in coalition with the Conservatives in 2010.

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

Appealing to moderates from other parties to join the Lib Dems, he said there was a risk of emulating the People's Front of Judea and the Judean People's Front from Monty Python's The Life Of Brian - two almost identical forces competing in the same ground.

He added: "I make the case that it is much easier under our electoral system to work within existing party structures and with people who have shared values, rather than trying to compete.

"As the old adage has it: we hang together, or we hang separately."