In the South of England and London, the Tories are winning votes from both parties. In safe and leaning Labor seats where the second party is the Liberal Democrats, their is a drain from Labor to the LD, everywhere. In the West of England, the Tories are eating away at LD. It seems more of an anti Labor vote swing than anything else. But the Tories didn't move outside London and South and West England, and thus not that many seats will change.
This election would have been a lot more interesting if they did proportional rep. in UK...
There is more tactical voting by the way than at any time in British history. National swing analysis matters less in this election than any other that I can remember.