Boris Johnson has issued a Brexit challenge to Jeremy Corbyn ahead of their first head-to-head TV debate of the election campaign.

In what could be a defining moment of the election campaign, during a one-hour programme the two leaders will clash on Brexit in the first half hour and then other issues.

And just hours before the debate, the prime minister has written to the Labour leader posing a series of questions about his Brexit policy and accusing him of ducking them in the campaign so far.

"This election is about breaking the deadlock in parliament that has prevented us from getting Brexit done and working in the interests of the British people," Mr Johnson writes.

"The public have a right to know where the two candidates for prime minister stand on the big questions facing the country at this election. So far in this campaign, you have ducked those questions."

He challenges Mr Corbyn:

-You are proposing a second referendum on EU membership. In that referendum, would you recommend the UK should remain or leave?

-Your previous manifesto promised to end freedom of movement, but following your conference it is now Labour Party policy to "maintain and extend" free movement. Would you end, maintain or extend free movement, and would immigration be higher or lower under Corbyn's Labour?

-Asked on Sunday if you were prepared to continue to pay into the EU budget on an ongoing basis, you replied "clearly if you want access to a market there are costs involved". How much would you be willing to pay into the EU budget in return for "access to markets"?

-All 635 Conservative candidates standing at this election have pledged to me that, if elected, they will vote in parliament to pass my Brexit deal. Can you guarantee that every Labour candidate supports your Brexit policy?

Mr Johnson concludes: "Without satisfactory answers to these questions, the public will have no choice but to conclude that Corbyn's Labour, propped up by the SNP, will mean dither, delay, and uncertainty with two more chaotic referendums next year. Only the Conservatives will get Brexit done so the country can move on."

There is no place in the debate for Jo Swinson, after the Liberal Democrats and the Scottish National Party lost a High Court challenge against ITV over its decision to exclude their leaders.

Protesting, a furious Ms Swinson said: "There are millions of people in our country who want to remain in the European Union, a key issue in this election.

"So to have a debate just between two people who want to leave the EU leaves out a whole side of that debate, leaves out and silences the voices of millions of people in this country."

While this is the prime minister's first TV debate as Tory leader, he debated against his leadership rival Jeremy Hunt in July and took part in high-profile TV debates during the 2016 EU referendum campaign.

Mr Johnson's allies back the decision to hold a debate with just the prime minister and leader of the opposition and to exclude the Liberal Democrats and SNP.

"We broadly have a two party system," business minister Kwasi Kwarteng told Sky News.

"Credibly only two people are going to be, or are likely to be prime minister, Boris Johnson and Jeremy Corbyn.

"It's important the electorate see the two on offer. Nicola Sturgeon cannot be prime minister. The SNP are not even standing in a majority of seats. Jo Swinson's chances are very small."

Although Mr Corbyn took part in a seven-way election debate in 2017, he has yet to go head to head with a Conservative leader. But he goes into this debate trailing Mr Johnson badly in personal approval ratings.

The big year for TV election debates was 2010, when Sky News, ITV and the BBC each staged debates between Gordon Brown, David Cameron and Nick Clegg.

But there were no head-to-head debates between the leaders of the main parties in the 2015 or 2017 general election campaigns.

Sky News and Channel 4 broadcast "The Battle for No. 10", featuring interviews with Mr Cameron and the Labour leader Ed Miliband. There was also one seven-way debate including the leaders of smaller parties.

In 2017, Theresa May refused to debate with Mr Corbyn or other party leaders and her place was taken in one TV debate by then-home secretary Amber Rudd.

Just before she left office in July, Mrs May admitted she should have taken part.

Mr Johnson, who took a break from campaigning on his battle bus to prepare for the debate, is determined not to repeat the mistakes of the Tories' 2017 campaign.