This is probably a nationwide deal, and stock that has been left over from the BOGOF that was recently in place.
I was in my local Morrisons (Maidstone) and that had loads of Disney DVDs for £4 in a bin, at the Audio Bar area. Morrisons are quite sporadic though, so you may find the bins littered throughout - it has POS on it though, so should be a proper offer.
From memory, DVDs included:
Princess and the Frog
Sword in the Stone
I think Bedtime Stories was also there, too. I will pop to Morrisons tomorrow and get a full list and photos.