They have more choice in Warsaw than they used to (more shelves full of products in the same amount of floorspace as there used to be). They've also added a bakery, so you can now get superb muffins, crumpets and the like.
If any PF member where to buy corned beef in Warsaw, information welcome :)
Why not just order this: britishcornershop/princes-john-west-corned-beef-large
Delivery is £12 (60zl) for up to 20kg. If you spend £100 or more, delivery is £6.