Sir Vince Cable has urged opponents of Brexit in other parties to join the Lib Dems to create a “more powerful force” in the centre ground of politics.
Ahead of the party’s conference, which starts on Saturday, its leader said it offered a home to “liberals, social democrats, progressive and centrists”.
He has proposed an internal shake-up to build a “movement for moderates”.
But he has also sparked leadership speculation by saying he will quit once Brexit is resolved or stopped.
The 75-year old former cabinet minister, who only took over last year, has not set a firm date for his departure but signalled that he is unlikely to stay in place beyond next year, if there is no snap general election.
On the first day of their four-day conference in Brighton, the Lib Dems will discuss the Windrush scandal, animal welfare and decentralisation among other issues.
But the event is likely to be dominated by questions over the party’s future direction, after Sir Vince – who will make his keynote speech on Tuesday – called for a major overhaul of its membership and election rules to counter claims it lacked popular appeal and was struggling to be heard.
His proposals, which are likely to be debated but not voted on at this year’s event, could allow people to join the party for free and non-members to vote in future leadership elections.
Most controversially, he has floated the idea of future leadership contests being opened up to people who are not MPs. The party currently has 12 MPs and Sir Vince was elected unopposed last year.
He told the Press Association that his party – which backs a referendum on the final Brexit deal – could provide a home to those “fed up with the extremes of the current Conservative and Labour parties”.
“Whether you see yourself as a liberal, social democrat, progressive, or centrist there is a home for you here, particularly as we fight Brexit together,” he said.
“I have made proposals to open up our movement to become an even more powerful force at the centre of British politics, standing up to power and privilege to bring fairness and opportunity for everyone.”
The party said 10,000 people had pre-registered their interest to become party members since Sir Vince announced the proposals earlier this month.