The offer on the Marks and Spencer website shows £649 but they are currently giving an extra £100 off on selected TV's, including this one (when you go to checkout).
WhatHiFi magazine gives this TV a 5* rating. Delivery is free to UK and says it can take up to two weeks however I ordered mine last friday and will take delivery tomorrow. Would have had it sooner, only work commitments prevented it.
For an added bonus, you can buy through quidco for an extra 5% off.
As far as I know the offer is on for another two weeks. This is the cheapest I've found it.