The centrist Liberal Democrats have seen their political fortunes wane dramatically since 2010 when they joined the Conservatives as a junior coalition partner in former Conservative prime minister David Cameron's government.

Five years later they were almost wiped out, losing 49 of their 57 seats, as voters punished them for backing Cameron's austerity measures and ex-party leader Nick Clegg's decision to renege on an election pledge not to raise university tuition fees.

The party will use the conference in Bournemouth on England's south coast to agree policies aimed at wooing so-called "bluewall" voters -- people in southern England who are Conservative-leaning but drifting away from the party.

The Conservative's Rishi Sunak, who only became prime minister last October, must call an election by the end of January 2025 at the latest.

At the last election in 2019, the Lib Dems pledged to stop Brexit.

But speaking ahead of the conference party leader Ed Davey said that was no longer on the table.

"We want Britain to be back at the heart of Europe but we're also realistic that's going to take some time," he told 5 News, adding that people "aren't talking about Europe".

The cost of green policies is expected to be a central background of the next election after Sunak on Thursday announced a major reset of the UK's strategy to achieve net zero carbon emissions by 2050 amid a cost of living crisis.

In its 2019 election manifesto, the Lib Dems promised to tax frequent flyers and set a highly ambitious target of generating 80 percent of electricity from renewables.

The policy would have required a massive acceleration in the construction of solar farms and wind turbines on land and at sea.

The Lib Dems currently have just 15 seats in the 650-seat Westminster parliament behind the Conservative Party (352 seats) and the Labour Party (196).

The party had traditionally been the third largest party in British politics but now has fewer seats than the Scottish National Party (44).

After the Lib Dems, the Conservatives will held their party conference in Manchester on October 1-4, followed by Labour in Liverpool on October 8-11.