It's not just the UK that's enjoying deep discounts at the moment. In Holland, A-Toys is offering 25% off all LEGO, and 45% off when you buy three sets, until 29th of September. (Thanks MrMonkey).
And in Belgium, Dreamland has 25% off all LEGO as well, also until the 29th of September.
Clearly these retailers want you to start your Christmas shopping early and are therefore competing heavily for your custom.
Update: it seems that most, if not all, LEGO stockists in these countries are running this promotion!