It's not quite true that Cameron had no competition to his right. Perhaps they're akin to the Birchers Bill Buckley wisely purged from our right, but there is a party, which claims to be to Cameron's right and may have cost him seats, the UK Independence Party Although it didn't win any any in the House of Commons this time, the UKIP does have two seats in the House of Lords and, if Wiki is correct, some in the European Parliament. I've seen claims that had the 3.1% of the vote the UKIP drew this time gone to Cameron's party the Tories would have won the majority. With the proportional representation the UKIP want they'd have won 20 seats on their own. Of course with that the Tory's tally would have been 70 less seats, so you have to be careful for what you ask! I'm no expert on UKIP, other than knowing they've been accused of lots of things by the liberal press, but I'm not aware of them being accused of being leftists. So there is at least alleged rightist noise, if not seats, on Cameron's right.
BTW, with proportional voting Labour would also have 70 fewer seats, but LibDems would have had 92 more resulting in a Labour/LibDem majority coalition. I suspect they’re better off with the hung Parliament.