I never saw many American brands in the shops in southern England, but I haven’t been there for some time. When I did live there, I didn’t see any Nabisco. The British seem to have their own brands. I did see Mars candy bars.
I’m not the best person to answer since I haven’t been shopping in Britain for about fifteen years. Living in the UK, while different from living in the US, is so much more like the US than continental Europe, which took me quite some time to get used to. I missed so many of the American conveniences in Europe.
What I did love about living in England, and even Switzerland, was the history, the ancient places, and the lack of extremes in the climate. The UK is so picturesque, and I love their gardens and the way most of them love animals. I would love to have a nice, crowded, English garden, but not enough to move from LA! If one likes snow, the mountains of Switzerland are uncommonly beautiful, and the country is the cleanest country I’ve ever seen. The Glacier Express from Zermatt to St. Moritz is a beautiful, beautiful trip.