There are plenty Polish shops around London. The key is which to choose for the best products and what is worth trying.
When I left Poland to come to live in England, I didn't think I would miss the cuisine, but I also didn't expect that the products between continental Europe and England would be so different. For this reason, I like to venture out and buy some gems from my homeland from time to time.
Thankfully, London has much to offer when it comes to Polish food, thanks to a long history of Poles living in London and also thanks to the modern immigration of early 21st century.
Most of the (best supplied) shops can easily be found in parts of London, where there are the biggest groups of Polish people, like in Ealing and Shepherd's Bush, Streatham, Willesden and Wembley. Also in Shepherd's Bush is a Polish bistro – "Mleczko", with traditional home-made food – perfect for a simple dinner.
Once you decide to go to a Polish shop, you will be probably be wondering what to choose from the shelves. Most of the things will appear similar to what you can buy in other shops and supermarkets but remember their value is hidden inside. I do recommend you to buy Polish meat, not only minced beef, pork (Polish: schab), but especially the ham. In a Polish shop you can see everything displayed in the fridge and choose from a wide range of different hams and sausages.
I suggest trying Polish juices, especially carrot with additional fruit, which is made without added sugar. They are thick and tasty – perfect to drink as a dessert after a meal. You can buy them in 1L packages to take home or in small 330ml bottles to take to work or university.
Other things you may want to try are pierogi (dumplings), either frozen or ready to eat. I recommend ruskie (with potato, onion and cheese stuffing) or with cabbage and vegetables. Also worth considering are soft cheeses, mayo and bread.
As this is a rough guide, you may always want to take a friendly Polish "guide" with you to choose particular (read: the best) products. Good luck!