David Ruffley has been bursting through his shirt to warn Dave he could face a leadership challenge if he doesn’t deal with UKIP in time for next year’s Euro elections, so these numbers won’t make for happy post-holiday reading for the PM. An OpenEurope/ComRes poll has UKIP topping the bill on 27% among those certain to vote in 2014, and still breaking the 20 point mark for the general election. The key number for Dave: two-fifths of Conservative voters from 2010 would vote UKIP in a European election if it were held tomorrow…