Nigel Farage, leader of the anti-European Union, UK Independence Party (Ukip) said on 17 March his party could form part of a coalition government with the Conservatives and Northern Ireland's Democratic Unionist Party.

However, he wants guarantees from Conservative Prime Minister David Cameron that a referendum on Britain's European Union membership would be held this year.

Speaking after launching his new book The Purple Revolution, The year that changed everything, Farage talked of how the two smaller parties could co-operate.

"The DUP have got eight seats in Westminster at the moment, they're going to come out with eight, maybe nine, next time round, and there would be some points... we're different parties, but in those circumstances, there would be some points of agreement between us and the DUP, particularly on the referendum and the need to make border controls a really important issue,'' he said.

Farage believes Ukip could contribute over 10 seats to a possible coalition total.

''We're confident we will win a handful and I think we can get it into double figures. That's what I have said, they are the markers I've set. If things go right we can exceed that,'' he added.

Prime Minister Cameron has agreed to hold a referendum on Britain's membership of the EU in 2017, if his Conservative party win the general election on May 7. The Ukip leader however, would want to push for that to happen this year and accused the Prime Minister of wanting to backtrack from his original pledge.

''Well I'm sure Mr Cameron would love there to not be a referendum next parliament. That would suit his book absolutely perfectly, it's rather like the debates isn't it? They call for it but don't really mean it, and that is where Ukip comes in. If Ukip has a big election and does well and there is a good number of Ukip MPs and DUP and some others that helps Mr Cameron get over that magical figure, then there will be a referendum,'' he said.

The Ukip leader also bemoaned the impact of American style 'attack' politics, a key theme emerging from the rival Conservative and Labour party campaign styles for the 2015 election.

Labour hired US election strategist David Axelrod, who served as chief strategist and media advisor in Barack Obama's 2008 presidential run. Jim Messina, the Obama campaign manager for his 2012 successful re-election, is working for the Conservative party.

''We're going down the route of negative campaigning. It's not vote for me. It's don't vote for this drunken, womanising, crook. Do you know something? I was just in Washington recently and I said to people; Why do you do this? And they say because it works. Well, maybe in America it does. I don't think it works here. Do you know something? I hope it doesn't work here,'' said Farage.

Ukip, which has two lawmakers in Britain's 650-seat House of Commons and won last year's European elections in Britain, is set to split the right-of-centre vote on 7 May, threatening Prime Minister David Cameron's chances of re-election.

Current polls show Nigel Farage, a member of the European Parliament since 1999, has a strong chance of winning in South Thanet in Southern England despite it being held by Cameron's Conservatives for 117 of the last 130 years.