ES News email The latest headlines in your inbox twice a day Monday - Friday plus breaking news updates Enter your email address Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid You already have an account. Please log in Register with your social account or click here to log in I would like to receive lunchtime headlines Monday - Friday plus breaking news alerts, by email Update newsletter preferences

Liberal Democrat membership rules will be overhauled to allow moderates outside the party to help choose the next leader, Sir Vince Cable will say.

“Liberal-minded" voters will be allowed to sign up for free under plans to bolster membership, the former Cabinet minister will announce.

The Lib Dems have languished in the polls and struggled electorally since going into government in a coalition with the Conservatives eight years ago.

Sir Vince will say he wants to create a "movement of the moderates" that will bring together voters that loosely identify with the party.

At a speech in London, he will say: "We should widen membership with a new class of supporters who pay nothing to sign up to the party's values.

"They should enjoy a range of entitlements, including the right to vote for the leadership and to shape the party's campaigning online.

"The Liberal Democrats already have an army of voluntary helpers and deliverers, as well as 200,000 online supporters, who loosely identify with us and campaign with us, but currently have no say in the direction of the party."

It is widely expected that he will address leadership of the party in the speech. Sir Vince has reportedly told his MPs that he does not intend to remain as leader long term.

The speech come ahead of the party's annual autumn conference, which begins on September 15.

He will say: "Whatever rights our new supporters gain, we as a party aim to be in constant conversation with them, engaging them in campaigns and urging them to begin campaigns of their own.

"I want these not to be just about stopping things but about growing support for the things that matter to Liberal Democrat voters, and to the vast swathe of voters in the centre ground whom we are yet to persuade.

"Groups like More United, 38 Degrees, Avaaz and Change.org have shown us how these regular conversations can happen, how we can engage hundreds of thousands of people online.

"I want our party to do that and to offer our movement a political arm within Parliament. So it is not just a protest group banging at the door, but a movement with a voice on the inside - our parliamentary party."

Labour reformed its membership rules under Ed Miliband but the changes led to claims it had fuelled "entryism", where members of other groups infiltrate a party to subvert it with their own agenda.

Sir Vince will add: "The Liberal Democrats are not a socialist party concerned with extreme-left entryism or a right-wing party trying to keep out extreme right-wingers.

"We are a centre-ground, pro-European, liberal and social democratic party, welcoming like-minded supporters.

"This will be a movement for moderates."