I made my first pilgrimage to the Whole Foods shop on Kensington High Street -- the first Whole Foods outside of North America. The first adjective that comes to mind is: WOW!
Whole Foods is a proper American supermarket. Three stories total. The top floor is a giant food court with restaurants serving great sushi, pizza, crepes, seafood, Middle Eastern and other cuisines. There is even a small pub that serves SIERRA NEVADA BEER....ON TAP!!! You could come here for breakfast, lunch and dinner!
All the products are billed as organic and natural. No processed foods here. The butcher and fishmonger serve the freshest meats I've seen in London. The veg and fruit are all fantastic. They have quite a few Whole Food brand American foods like peanut butter, cereals, ingredients, pancake mix, syrups, jams and jellies, etc. The beer aisle stocks Sierra Nevada and Sam Adams (by the case!!), Anchor Steam and a few other American brewery choices. The extensive wine section has a good selection of California wines.
That said, Whole Foods is expensive. Much moreso than your average Tesco or Sainsburys. But then, you get what you pay for.