To add to Jeremy Corbyn's explanation of Labour's plan for business in the UK, we've outlined the 12 key policies in the party's 2019 election manifesto.

It was released yesterday with the slogan It's Time For Real Change.

The full document , externalruns to 105 pages. But what are the promises that will grab the public's attention, and potentially win over voters on polling day, 12 December?

Find out here.

The next questioner is also very tough on Mr Corbyn - he says he's "terrified" and "doesn't buy the nice old grandfather" image.

He thinks Mr Corbyn has supported hecklers who've attacked female politicians.

Jeremy Corbyn says bad behaviour, misogynism, racism, is "not acceptable in any form in our society or my party".

The questioner comes back again, saying female Labour MPs need protection - why?

Host Fiona Bruce moves things on.

Iain Watson
Political correspondent

Jeremy Corbyn is lagging in the polls and really needs to challenge negative perceptions of him this evening, if he is to beginning to turn things round - the election clock is ticking loudly.

The first reply is stinging - the audience member says he's afraid of Mr Corbyn's "reckless" policies and fears for the impact on areas like free speech and human rights.

The Labour leader says he doesn't understand the questioner being afraid of his policies, but he wants to live in a country with a stronger health service, better schools, and so on.

Jeremy Corbyn says he's spent his life defending people's human rights and freedom of speech - and says he has "got into hot water" for doing it.

Bringing industries like water back into public ownership will give consumers and workers more power to run them, he adds.

Iain Watson
Political correspondent

Jeremy Corbyn denounced billionaires and bad bosses when he launched his manifesto, but has the opportunity tonight to say business should not be frightened by the prospect of a Labour government.

Quite a bit of cheering for Jeremy Corbyn as he walks out. He's all smiles.

Now, question one - should businesses be frightened of a Labour government?

No, says My Corbyn.

He says the biggest businesses will be asked to pay more, but small and medium-sized firms, who make up most of the economy will see huge investment.

Things like broadband, apprenticeships...

"I enjoy working with all the business organisations," Mr Corbyn says.

Labour leader Jeremy Corbyn steps out onto the stage. The audience is ready to go and will have half an hour to grill him.

Here we go...

With the leaders' event just starting, Boris Johnson is yet to arrive... but don't worry he's got a bit more time than the others.

He's going to be the last of the four leaders to make his pitch tonight - so will be on our TVs at 20:30 GMT.

Tonight, the BBC is hosting this special edition of Question Time. The leaders of the Conservatives, Labour, the SNP and Liberal Democrats will take audience questions for 30 minutes each.

What other election TV specials are still to come?

• 29 November: Seven-way debate featuring representatives of all major parties from Cardiff airs on BBC One
• 6 December: BBC One hosts final head-to-head debate between Conservative leader Boris Johnson and Labour leader Jeremy Corbyn

Image source, Getty Images

• 9 December: Emma Barnett presents a BBC Question Time special focused on an audience made up of young voters under 30

• Before 12 December: Channel 4 News to host a debate focusing solely on climate change. Labour, the Liberal Democrats, the SNP and the Green Party have all agreed to take part, but the Conservatives not yet said whether they will attend. A date is yet to be announced.

Boris Johnson is going last and there's some benefit to that, says Jo Tanner, former Conservative Party strategist. Not least because you get to hear what everyone else says about you and then you get to respond to it. To have the last word.

But she adds, on the other hand, the audience might well be somewhat fatigued by then - they may be restless, sick of hearing well-rehearsed lines, and emboldened to ask the final person up the toughest questions of all.

Election promises have been coming thick and fast this week as parties release their manifestos.

We've been keeping track of them all in our concise guide here, which shows you where the parties stand on big issues like Brexit, education and the NHS.

Nick Clegg in 2010 is widely seen as the person to have really shot into the political stratosphere as a result of a TV debate - remember that brief period when it seemed like the whole nation "agreed with Nick"?

Polly Mackenzie, former special adviser to Nick Clegg, says her man was in a fairly easy position in 2010 - he could be the new guy and just keep referring to the "two tired old parties".

David Cameron and Gordon Brown knew Nick Clegg was going to get all the best lines, she says.

Beyond that, though, he did actually do a good job, she thinks - he created a sense of connection with the audience, told stories, made people laugh.

Image source, Getty Images

If tonight's special edition of BBC Question Time leaves you feeling passionate about the election on 12 December, remember, there's only four days left to register to vote.

You can get all the information you need about registering to vote here.

BBC political correspondent Iain Watson tells the presenter Christian Fraser that he's looking for a memoriable moment - remember Ed Miliband taking a bit of a stumble when he did a similar event in 2015?

Beyond that, our political correspondent says, he'll be looking for different things depending on the leader.

Will Jeremy Corbyn talk about some of his radical policies? Will Nicola Sturgeon talk about her red lines on offering SNP support to another party?

Will Jo Swinson, the newest face on the block, "cut through" as the Westminster saying goes? Will Boris Johnson, currently leading in the polls, slip up?

Here's a brief guide to Question Time for viewers old and new.

Question Time is a topical debate programme in which guests from the worlds of politics and the media answer questions posed by members of the public.

It is hosted by Fiona Bruce, who became the first female full-time host in the show's 40-year history after David Dimbleby left the show in December 2018.

Each week Question Time aims to select a panel with a broad range of views, knowledge and experience, with panellists who are relevant to the big stories or debates of that week.

Tonight the leaders of the UK's four major parties, Boris Johnson, Jeremy Corbyn, Jo Swinson and Nicola Sturgeon, will appear on the programme for an election special.

In a change from the usual format, each leader will take turns answering questions from the audience for 30 minutes.

BBC political correspondent Iain Watson will be in the "spin room" tonight keeping us up to date with all the reaction to the leaders' performances.

What exactly is the spin room? Well, it's an area where journalists can interview the leaders or their representatives after the event.

Not long to go now until leaders of the Conservatives, Labour, Liberal Democrats and the SNP face questions from the BBC Question Time audience in Sheffield.

So what could come up during the two-hour television special?

Brexit

Three and a half years after the EU referendum, two prime ministers down and with Parliament deadlocked, Brexit remains hugely divisive.

The NHS

All of the parties agree the NHS needs more money but a row is likely over whether the NHS would be included in trade negotiations after Brexit - a criticism directed at Boris Johnson by Jeremy Corbyn a number of times previously. Mr Johnson has said the NHS "will never be for sale".

Climate change

We've heard a number of "green" pledges in this election so far - so this is another issue the leaders are likely to be quizzed on.

Scottish independence and coalitions

Nicola Sturgeon is bound to talk about this issue, as the SNP want a referendum on Scottish independence in 2020.

Both the Conservatives and the Liberal Democrats have said they would block a second vote. If the Lib Dems were in a position to form a coalition, they have suggested they would request another referendum on Brexit.

Read more: How to watch the BBC Question Time leaders' special

Jeremy Corbyn stopped to wave at supporters as he arrived for the Question Time leaders' debate in Sheffield.

Some of the crowd cheered and started chanting "Oh Jeremy Corbyn" as he made his way into the building.

Jo Swinson and Nicola Sturgeon arrived before him, so we're now just waiting for Boris Johnson...

You can check the latest opinion poll trends ahead of this evening's Question Time special with our poll tracker.

It measures how people say they are going to vote at the next general election.

Find the poll tracker here.