British Prime Minister Boris Johnson says he’s nervous about his narrowing lead in opinion polls before Thursday’s election but pledged to deliver a “transformative” Brexit on January 31 that would allow lower immigration.

The December 12 election will decide the fate of Brexit and the world’s fifth largest economy with a stark choice between Johnson’s pro-market Conservatives and the socialist-led opposition Labour Party.

“Brexit is the most radical and profound change to the management of this country,” Mr Johnson told Sky, adding he would lead the United Kingdom out of the EU on January 31 if he won a majority in the 650-seat parliament.

“Brexit is indispensable. You can’t move forward without Brexit,” said Mr Johnson, the face of the ‘out’ campaign in the 2016 referendum who won the top job in July after Prime Minister Theresa May failed to deliver Brexit on time.

Voting begins at 7am, local time, on Thursday and polls close at 10pm, when an exit poll will give the first indication of who has won.

Mr Johnson will likely need more than 320 seats to ensure he can stay prime minister and ratify the Brexit deal he struck in October.

Opinion polls, which largely failed to predict the 2016 referendum result or May’s loss of her majority in the 2017 snap election, show Mr Johnson leads Labour Party leader Jeremy Corbyn, though the lead has narrowed in recent weeks.

Asked if he was nervous about narrowing polls, Mr Johnson said: “Of course, we are fighting for every vote. I think that this is a critical moment for this country.”

Four opinion polls published on Saturday put the lead of Mr Johnson’s Conservative Party over the Labour Party at between eight and 15 points.

No major poll shows Mr Corbyn, a committed socialist who wants to bring swathes of the British economy into state ownership and raise taxes on the financiers of London, will win.

But Labour could still lead a minority government if it deprives Mr Johnson of a majority as few other parties are willing to prop up a Johnson government.

Labour proposes negotiating a new deal and then holding another EU referendum.

Mr Johnson dodged a question on if he would resign if he failed to win a majority and dismissed questions suggesting that after nearly a decade of Conservative-led rule, he was offering little to voters beyond Brexit.

“Trust in politics has been undermined,” he said.

“It’s been undermined by people who for three and a half years … promised to deliver Brexit and then didn’t.”

Echoing the Leave campaign pledges of the 2016 referendum, Mr Johnson promised lower immigration with a points-based Australian-style system.

“Numbers will come down because we’ll be able to control the system in that way,” Mr Johnson said, adding that his focus would be cutting down on unskilled migration, but that there would be scope for high skilled and other workers to come to Britain.

When asked by Sky what the naughtiest thing he was ready to admit to was, Mr Johnson initially asked advisers for suggestions before saying: “I think, I, you know, I may sometimes, when I was riding a bicycle every day, which I used to do, I may sometimes have not always have obeyed the law about cycling on the pavement.”

-AAP