It's been a busy morning and one mostly dominated by leaders' debate-related chatter. Here's a quick round-up of what's been happening so far:

• UKIP leader Nigel Farage told BBC Radio 4's Today his party would have a cap of 50,000 people a year coming to Britain, but insisted there would be no cap on net migration
• The main TV debate of the election will be held tonight , with David Cameron and Ed Miliband sharing the podium with Nick Clegg, Nigel Farage, Leanne Wood, Natalie Bennett and Nicola Sturgeon. The debate will run for two hours and cover four topics, which have not been revealed
• In his regular LBC phone in, Lib Dem leader Nick Clegg suggested the debate is an opportunity to see who you want to walk into Number 10 with David Cameron or Ed Miliband
• Labour has a letter in the Guardian endorsed by 100 people from "all walks of life", including actors, business leaders, writers, nurses and low-paid workers. The letter argues that the fundamental choice at the election is whether the country works only for those at the top or for all working people
• The Muslim Council of Britain has drawn up a list of key commitments they suggest Muslim voters may wish seek from would-be Mps, including "meaningful action" to combat Islamophobia, anti-Semitism and all forms of racism.

Reacting to Nigel Farage's earlier comments on an immigration cap, James Brokenshire, an immigration minister, said: "Nigel Farage makes up his policies as he goes along. One moment it was 50,000, then it was 30,000 and then there was nothing at all. It’s very difficult to put any credibility on anything that UKIP say."

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Ed Miliband is now taking questions from the audience. Friendly questions so far, including one praising the Labour leader's performance when he was being questioned by Channel 4's interrogator Jeremy Paxman.

Labour leader Ed Miliband is now conducting one of his people's question time sessions in Bury.

BBC's Labour campaign correspondent Iain Watson says that Mr Miliband will be visiting the debate set this afternoon - but not at the same time as his opponents.

Aides insist he is no more nervous than he would be appearing at his regular People's Question Time events. But he has certainly had more practice - mostly with his own staff though also with Alistair Campbell, Iain adds.

Carole Walker
Conservative campaign correspondent

David Cameron spent much of yesterday preparing for tonight’s debate and after a campaign visit to a school this morning he will continue the process. Aides point out that he can already draw on the experience of the weekly sessions of Prime Minister’s Questions and more than one hundred of the Cameron Direct meetings with the public which he has held around the country since he took power.

The leaders drew lots for their positions and Mr Cameron will be on the far right of the line-up. That suits his strategy of trying to portray himself as the Prime Minister who’s long-term economic plans have turned around the economy versus the chaos which he says would result if any combination of his rivals ends up in power. There is the danger though that they will all gang up on him forcing a slip-up or unfortunate phrase. Under the harsh lights of the TV studio he can expect little sympathy.

BBC News Channel

The SNP's Angus Robertson says the format of tonight's debate is not going to provide a knockout blow or one winner over six others - but it will be an interesting shop front, for people to see SNP leader Nicola Sturgeon.

"Like all politicians she's been preparing for the debate," he says - and she's been talking to advisers about the different dynamics and how you can use your time effectively to get your message across, he says.

You'll be able to watch Nicola Sturgeon at first minister's question time in Holyrood at 12pm.

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Sky News

UKIP leader Nigel Farage has continued his tour of the media studios this morning, appearing on Sky News a little earlier. Asked about tonight, he said: "I'm feeling pretty good and I'm pleased at least there is a debate." He said he'd be asking the prime minister and other party leaders to admit that, as members of the European Union, "we cannot have an immigration policy of any kind at all".

BBC News Channel

Conservative campaign correspondent Carole Walker, on the Tory campaign bus, says the team is on its way to a school in the north-west. She says the Conservative leader will spend much of the day resuming preparations for tonight.

David Cameron is going to be on the right of the line-up of leaders and Carole says she's been told he's pretty happy with that position. The strategy is for Mr Cameron to repeat the message that "you have a long-term economic plan with me as prime minister".

BBC Radio 5 Live

Ever wondered what the leaders' debate would be like if it was a game show? Well, wonder no more. "Voice of the balls" Alan Dedicoat introduces the contestants for tonight's show.

BBC News Channel

From Bury, the BBC's Labour campaign correspondent Iain Watson reports on the Labour leader's movements ahead of tonight's big event.

Ed Miliband is doing a People's Question Time event this evening - the best way to practice ahead of the debate, perhaps? Iain says about the leaders' debate itself: "He knows it is crucial. The main thing is not to mess up and not to set a negative tone for the remaining five weeks."

BBC Radio 4 Today

If you missed Nigel Farage's interview on the Today programme earlier, you can watch (it's on webcam) the whole thing back here. The UKP leader was challenged over his party's policy on immigration and problems encountered with candidates.

LBC

In the final moments of today's Call Clegg, LBC presenter Nick Ferrari offers the Lib Dem leader some pointers for tonight's debate. He suggests he should open with a joke, "perhaps a dirty gag", roll his eyes, generally look disinterested, "and some fruity language whenever you can". Nick Clegg admits he was intending to pursue a different approach, but he says he'll take his advice on board.

We'll be watching...

LBC

Asked about Wednesday's Telegraph letter by business leaders, Nick Clegg notes that the signatories said the greatest risk to the economy was a departure from the course set over the past five years. I agree with that assertion, he says, but I strongly disagree that a Conservative-only government would maintain the current course,as they want to "lurch off" to a different direction and impose ideological cuts to spending.

The Muslim Council of Britain estimates there are more than 40 constituencies where the votes of Muslims "can make a difference" to the outcome.

The document, Fairness Not Favours, quotes the 2011 Census, which puts the Muslim population in England and Wales at 2,706,066 (with 77,000 Muslims in Scotland and 4,000 in Northern Ireland). There are 26 parliamentary constituencies with a Muslim population of 20% or more. There is also a sizeable Muslim presence in several marginal constituencies.

LBC

Nick Clegg goes head-to-head with a caller over the coalition's commitment to spending 0.7% of national income on international development aid. The caller isn't happy with the policy - and says British taxpayers don't want their money being spent in that way. "We're not going to agree on this, but you can't dismiss it as total rubbish," Mr Clegg responds, adding: "You can have your views but don't claim you're speaking for absolutely everybody."