The millions of EU citizens in the UK should be barred from voting in any referendum on whether Britain should leave it, Nigel Farage has said.
The Ukip leader said he would insist on this as an essential condition to any coalition deal with the Tories after the next general election.
"We could potentially do a deal with Mr Cameron on this but not unless the timing and the terms of the referendum were right," he told Andrew Marr on Sunday.
"I want a guarantee that in this referendum the only people that can vote are British citizens because at the moment there are four million or so EU citizens living in Britain who I do not think should be allowed to vote in that referendum".
EU citizens living in Britain cannot vote in general elections but they can vote in local and European Parliament polls.
Farage added joining a coalition was "unlikely", saying: "I don't think the lure of a ministerial car is the reason I got into politics".
He also said he would not do a deal with Ed Miliband without a firm commitment to an EU referendum.
He also told Marr Ukip would pledge £3 billion to running the NHS, which would be saved once Britain left the EU.
"We want the NHS to be better run, we want it to be more efficient. We think it's ludicrous that middle management has grown by 48%, we think the fact that health tourism is costing £2 billion a year is wrong and the fact that one in five new nurses being taken on have to come from abroad says to us 'let's make sure there are no tuition fees for people who are taking medical degrees'.
"We want a National Health Service that is free at the point of delivery and funded through taxation.
"But the one thing nobody dares say is the reason we have an NHS crisis right now is because of a massive increase in the population in this country."
He added: "We would promise an extra £3 billion a year for the National Health Service funded out of the fact that we will not be paying daily membership fees as members of the European Union."
Mr Farage stood by his previous comments that people with HIV should not be allowed to come to the UK to seek treatment, adding that the same should apply to all other areas of health including maternity services.
He said: "I very much take the view that it is a National Health Service, and to open ourselves up - whether it's to HIV treatment, whether it's to maternity services or whatever it is - to the rest of the world, doesn't make sense. It is costing us at least £2 billion a year, the National Health Service is here for British citizens."