A variation on the M and S cava deal. Pinot Grigio is normally £4.49 per bottle but is currently on 3 for £10. If you buy 6 the till takes 25% off the full price, then applies the 3 for £10 discount so the total comes to £13.26.
They also have the Las Falleras red, white and rose (normally £3.99 per bottle) on the 3 for £10, presumably the 2 reductions would also work on these.
(Thanks to whoever added the photo, but it's not that particular pinot grigio bottle which is on offer, there isn't a photo of it on the M and S site).