Asked if he still thought that UKIP voters are "closest racists, loonies and fruitcakes" the Prime Minister told ITV News: "We live in a competitive, political world and people make their choices. I'll choose my words carefully. I want people to support my party.
"I'll let people make up their own minds but at the end of the day, at the next election there is going to be a very straight choice. It will be a red, blue choice."
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"My sincerest apologies to everyone who purchased tickets and were planning to come to the upcoming shows."
His comments at the Defence and Security Forum on Monday came after a £20 billion black hole in the budget for the next decade emerged.
The Foreign Secretary said he thinks the health service should be "at the very top of the list" for a windfall after the UK leaves the EU.