Tesco have several Lego and Duplo Boxed sets half price, but they also come under the 3 for 2 toy promotion on at the moment.
I picked up 3 x 200 piece duplo which usually retail at £50, for £50 total (less than £17 each).
Both lego and duplo were available in 2 sets, one XXL set for £50 reduced to £25 - and a smaller booster set around £13 down to £6.50ish. The sets were vaguely plain featuring mostly coloured blocks, but the bigger ones had a few feature blocks such as windows.
I've had a quick look on their website and cannot see the sets featured instore... I picked these up in the Hamilton store in Leicester.
Im sorry to be vague on the details. In a rush and just wanted to give you guys a heads up.
My first post so be kind - havent got time to put a pic up this second but hopefully later tonight if no one else is able to.