At my local Tesco (Westwood Cross) they had a £5 off a £25 spend leaflet as you entered the store and also from the Click and Collect desk.
The leaflet said Westwood Cross store only, but I'd imagine this must be in other stores too?
I used it to get £5 off a £25 Game, and I had a second run to get some money off pillows and towels.
I think the voucher had an expiry date of 11/01/15, but I don't have one in front of me right now
Confirmed in the following locations:
Westwood Cross - by Eldini - Expiry Date 11/01/15
Leyland - by v6boy - Expiry Date 31/12/14
Sunderland - by Boldonglen
Carmarthen - by cashandben
Please post or edit this first post if you find it available in your local