Nigel Farage is expected to press "no" campaigners to make a positive case for Britain's EU exit to boost their chances of referendum success.
The Ukip leader also wants to see David Cameron's renegotiation approach challenged, including over issues such as border control, the sovereignty of Parliament and costs associated with EU membership.
These areas are viewed by Ukip as being among the main concerns of British voters, with Mr Farage due to use a speech in London to call for the "no" campaign to promote its case rather than argue about who should lead it.
His intervention comes after Mr Cameron insisted technical talks on the UK's demands for EU reform are going "quite well".
But the Prime Minister acknowledged there would be "road blocks ahead" in his drive to change the terms of the relationship with Brussels.
Discussions over renegotiating the UK's relationship with the EU ahead of an in/out referendum will go on throughout the summer.
They are expected to continue at least until the European Council leaders' summit in October, with the poll taking place before the end of 2017.
Mr Cameron has indicated it could be held earlier while the House of Lords EU Committee has suggested the Government would prefer it to take place in autumn 2016.
Chancellor George Osborne has also warned Britain must fix its economic relationship with Brussels to persuade the voters it is right to remain in the EU.
The senior Tory, who is playing a leading role in renegotiations in Europe ahead of the in/out referendum, said the central attraction of membership was the economic benefits and he preferred to talk about the EU as a "single market of free trade".
A university-led campaign aimed at backing Britain's EU membership has already been launched.
Speaking at this week's event, shadow business secretary Chuka Umunna said he would be "intensely relaxed" should Mr Farage emerge as the figurehead for the "no" campaign during the in-out referendum.
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