i dont pay much attention to polls, surveys and particularly to betting odds...they all in my view are directly or indirectly intended to manipulate a particular angle or a side.
when attempting to project anything vote-related, my 1st look would normally be at the structure (and trends) of the particular electorate. the uk today is not what it was during churhill, not even what it was more recently during thatcher or when it was called common market.
it is the electorate that put a muslim to the highest london seat, a country which had its migrant population more than double in two decades since the early 90s, a country that experienced waves of eastern europeans...in one word, the uk just like most countries on the continent has decidedly moved away from a homogeneous nation it once was towards a multicultural, multi-ethnic society...
perhaps it is a stretch, but a split in such a trend would seem an unnatural development. thus, everyone relax, they will remain. Probably.