They were an electoral powerhouse, the party of political titans Winston Churchill, Margaret Thatcher and Benjamin Disraeli. But Britain's once-towering Conservatives end their annual meeting on Wednesday with their very future under threat.

The Tories, as they are colloquially known, are languishing in opinion polls and risk being swallowed up by the hard-right Reform UK party.

"It is existential," political scientist Robert Ford said of the crisis gripping the United Kingdom's oldest political party, which was founded in the 1830s.

"On the current numbers, you'll be able to fit Conservative MPs (members of parliament) into a small coach after the next election," the University of Manchester professor added.

The Tories have run Britain for large chunks of recent history, including an 18-year stretch between 1979 and 1997 and 14 years from 2010 to 2024.

They have won more general elections and returned the most prime ministers of any modern-day UK political party, ruthlessly adapting to tap into the prevailing public mood of the time.

But the 2016 Brexit referendum sparked an unprecedented decline in the party's fortunes, triggering the resignation from Downing Street of then-prime minister David Cameron and unleashing bitter factional infighting.

The Tories cycled through another four leaders including Boris Johnson, who was brought down by numerous scandals, and Liz Truss, who was forced to quit after a disastrous budget, before Britons booted them from office in July last year.

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Conservatives are still enamoured with the late Margaret Thatcher, memorabilia of whom can always be bought at the party's conference / © AFP

"They've only got themselves to blame in a sense," Tim Bale, professor of politics at Queen Mary University of London told AFP.

"They made all sorts of promises on immigration and the economy, which they didn't deliver on in government. The public are rightly frustrated with them."

Last year's election, won by Keir Starmer's Labour party, saw the Conservatives reduced to just 121 lawmakers in Britain's 650-seat parliament -- their worst defeat in a general election ever.

Their fortunes have since fallen further as the anti-immigrant Reform party, led by charismatic arch-Eurosceptic Nigel Farage, outflanks the Tories on the right, eating into their support.

- Election wipeout? -

Leader Kemi Badenoch will on Wednesday seek to rally the Tory faithful during the headline speech at the party's poorly attended four-day gathering in Manchester, northern England.

This week she has announced that any future Conservative government led by her would take Britain out of the European Convention on Human Rights and deport 150,000 irregular migrants a year.

But with polls showing the next election, expected in 2029, gearing up to be a straight fight between Starmer and Farage, many people around Westminster are speculating she will be gone by then.

While the Conservatives have suffered heavy defeats before, notably in 1945 and 1997, they have always had time to rebuild against Labour -- a luxury the rise of Reform does not grant them today.

"The hole they're in is way, way deeper than any hole they've been in for a century or so," said Bale, who advises the Conservatives against trying to echo Reform on immigration.

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Empty seats have been a feature of this year's Tory conference in Manchester / © AFP

Several former Tory MPs, one sitting lawmaker, and dozens of councillors have defected to Reform in recent months as surveys show the Conservatives heading for a near wipeout at the next election.

A YouGov poll released last month found that if a general election was to be held now, the Conservatives would be reduced to just 45 MPs.

That would put it in fourth place, behind the centrist Liberal Democrats, with Reform just short of a majority on 311 seats.

If such a scenario followed the next election then Farage could ask the Tories to become a junior partner in a governing coalition.

Ford reckons that while some Conservative MPs and activists might find this tempting, they will be fearful of "a black widow spider effect".

"You mate with the larger one and it eats you," he told AFP.