Just popped into my local Tesco Express in Elm Park (Romford) and bought 'pop works & company' popcorn for 50p. On the label it was written £1 (was £1.54), went to the self service til and came up as £0.50, went back for another pack!
Initially went to buy this because could claim one bag free on Shop-mium.
Bought the peanut butter & caramel flavour and sticky toffee pudding.
Plenty left on the shelf near the til including: sweet & salty; peanut butter & caramel and sticky toffee pudding flavours.
A small error in store, deal is national.
Hope this helps someone.