Ukip leader Nigel Farage believes David Cameron cannot be trusted to deliver an in/out vote on Europe.

Farage said that Cameron's promise of a referendum on Britain's future in the European Union in 2017 is "not good enough," and his party has "changed the political agenda."

Speaking after Cameron's keynote speech, Farage cast doubt on whether it was even possible for the Conservative leader to renegotiate the terms of Britain's membership of the EU.

The Prime Minister said a referendum will be held after a new settlement with Europe on decision-making powers is struck after the 2015 general election.

However Farage told the BBC: "The difficulty is that [Cameron] is the same man who gave us a cast iron guarantee in the past, that if he was PM, he would put the Lisbon treaty to a referendum. He let us down, so I think the issue of trust is rather important."

"I do question how he's going to be able to re-negotiate our relationship in a roomful of people who are not inclined to do so."

Regarding his own party, Farage said: "What's new this morning is that the whole nature of the European debate has changed and that's good news. Ukip have been told that they represent a tiny minority view and frankly it shouldn't be discussed in front of the children."

Despite this attitude from those in government, Farage believes that, "if Ukip hadn't have been there this speech wouldn't have happened. We want to trade and co-operate with Europe, but we don't want to be part of a European union.

"Ukip has changed the political agenda. Now the battle-lines have been drawn."

Ukip has enjoyed a surge in popularity in recent by-elections on the back of polling figures showing a majority of UK residents want a new relationship with the EU. Polling predictions suggest the party is capable of collecting enough votes in swing seats to deny the Conservatives a majority at the 2015 general election.

However Conservative MP David Nuttall told IBTimes UK that Cameron has outflanked Ukip with his speech, and there is now "no reason for anybody to vote Ukip" in light of the Prime Minister's address.

Click here for the Eurosceptic MPs who helped force Cameron to offer in/out vote on EU.