Star Wars rise against the empire power disc pack £1 at Tesco Bramley Leeds. Was last on shelf there so not sure about availability elsewhere. Other power discs were still £4 or £5. Is referred to as PD55408 on my receipt.
For the benefit of unimaginative pedants I like most others am quite aware that many Tesco deals are not in every store but am posting for the many who understand this and may wish to check if they are visiting their local store.