shop from their ethnic food shops
Polish shops in the UK can be like that to a point. The6 even have stuff like Masmix spread. Margarine is identical from country to country so odd to buy it. Polish brands of coffee too, identical to coffee in any other shop for a lower price. The same with fruit juice. Those places tend to cater to the less adventurous, and I suspect many of them don't make much money. The bigger ones that do tend to be a. not just Polish and b. almost a social centre.
Not all Poles in the UK are like that though, some/most are more adventurous.
Worth mentioning that in my town in the UK (lots of post-2004 Poles there), a more upmarket Polish deli opened as well as a Polish craft bakery, both aimed at Poles. Both have gone bust now.
tikka masala chicken in Poland
Maharaja near pl. Konstytucji used to do a decent one. Most of the curries in Warsaw are inauthentic. Namaste on Hoża is probably the best, however I don't recall them doing a tikka masala which was invented for the U.K. market.
When Marks and Spencer had the food hall on Marszalkowska they did brisk business, especially baked goods. The customers there were a mix of British, people from other English-speaking countries, and mostly Poles.
If people want some food that suits British tastes, Makro isn't bad. They have lamb and also boczek of a type that you don't see in grocery shops, a type that substitutes quite well for bacon.