Just popped into local Morrisons (Wigan) and they had a display of blu-rays from £5. Most were £7 or more and old rubbish blu-rays, but they had 2 copies of Robin Hood for £5, bought one and left one on display. Not online, INSTORE ONLY. Not sure is nationwide (staff not very helpful as usual). It shows on the reciept as "DVD 5800" but definately blu-ray packaging and barcode. They could be clearing old stock?
Hope it helps someone.