British Prime Minister Boris Johnson (L) and British Labour Party leader Jeremy Corbyn shake hands during their election head-to-head debate live on ITV in Salford. Tens of thousands of polling stations are set to open on Thursday as British voters prepare to choose members of parliament in a snap election. File photo: Jonathan Hordle/IT.

London - Tens of thousands of polling stations were set to open at 7:00 am on Thursday as British voters prepare to choose members of parliament in a snap election called by Conservative Prime Minister Boris Johnson to seek a majority and "get Brexit done."

"Vote one-nation Conservative party, get Brexit done [and] move our country forward," Johnson said in a video message to voters on the eve of the "most important election in modern memory."

He campaigned on promises to withdraw Britain from the European Union on January 31 and cut taxes while funding improvements to health, education, police and rail services.

The deal he negotiated with Brussels is "oven-ready... to get Brexit done," if a Conservative majority can push it through a new parliament, Johnson said at a campaign event on Wednesday.

Johnson, 55, has also pledged to limit immigration and negotiate liberal post-Brexit trade deals with the United States and other non-EU nations.

"We're a great country and we can be greater still," he said in another campaign message on Wednesday.

The main opposition Labour party's left-wing leader Jeremy Corbyn offered a radical "manifesto of hope," promising to renationalize key industries, invest massively in infrastructure and provide free broadband services.

Corbyn, 70, promised that Labour would negotiate an improved Brexit deal to pit against remaining in the EU in a second Brexit referendum, and would then "carry out" whatever the majority decided.

He urged voters to save the national health service, which has been subject to cuts and privatization in recent years.

"We can rewrite the economy for the many, not the few," Corbyn said in a campaign speech. "It's time for real change."

About two-thirds of eligible voters, or more than 30 million people, are expected to take part in the election.

Most analysts believe a comfortable parliamentary majority for the Conservatives is the most likely outcome under Britain's constituency-based, first-past-the-post system.

A key opinion poll late Tuesday also suggested the Conservatives will win a majority of several dozen seats in parliament.

Johnson's predecessor, Theresa May, lost the party's majority after calling a disastrous snap election in June 2017.

The YouGov poll predicted the Conservatives will win about 43 per cent of votes on Thursday, with Labour on 34 per cent and the anti-Brexit Liberal Democrats on 12 per cent.

That would give Johnson a parliamentary majority of 28 seats, according to the pollster's seat-by-seat analysis.

Leading political analysts have warned, however, that a hung parliament remains possible.

Much could depend on the results in several dozen key marginals. Tactical voting could also play a part in a small number of seats where the anti-Brexit Liberal Democrats are competing for votes with Labour, or where veteran eurosceptic Nigel Farage's Brexit Party are vying with the Conservatives.

If the election does, however, lead to a hung parliament, Labour could win enough seats to form a minority government with support from the smaller Scottish National Party (SNP) and possibly the Liberal Democrats.