I've been into my local Asda in Cardiff and they currently have wine miniatures on offer at half price.
Most of these are down from £2 to £1, which means 3x25cl bottles = £3 around half the price of the full 75cl bottle which is bonus to start.
If that's not enough - the reason they have these miniatures in the first place is to entice you to buy the whole bottle. They promise to take the price of the mini from the full size if you take the receipt back. The thing is, even though you only pay £1, they will still give you £2 off the big bottle.
Enjoy, they've got some nice Casillero Del Diablo in mine.
They even have £1 of the big bottle before you begin applying any of the above.