Think about it. The reason the UK government made a show of preemptively denying Snowden entry to the UK is to avoid the insane dilemma it would have caused them. The US would have exerted pressure to extradite, and the hugely-skewed-in-US-favour US-UK extradition treaty would have made it almost certain an extradition attempt would have succeeded. On the other hand, the electorate would have been up in arms over it, and it would have been a huge political issue that the opposition would have seized upon; not exactly something a coalition government needs.