Didn’t Cameron already promise a referendum? He’s threatening that he may not find a Boehneresque way to cancel the vote if they put Juencker in
Cameron promised a referendum back in 2009 and broke that promise. His next promised referendum is supposed to be for 2017, eight years after he’s done a pile of damage to the UK by being a “liberal conservative” especially over the gay marriage debacle, another thing he lied about (voted against last year, but now is saying that it will make British society stronger if you can believe that).
Jean Claude Juncker is on record as saying “When it gets serious, you have to lie”. Cameron is no less a liar, but not an admitted one.