They are an ericaceous plant, Diane, and grow on British moorlands. The ones in the shops are a cultivated variety with larger berries than the native plants. They can be grown in gardens but you would probably need quite a few plants for a decent crop, hence the high price of the berries.

Sainsbury's!

Didn't know they grew naturally in UK - thought they were a US import like blueberries.
Take a look at http://www.pots2plots.com/Fruit/Growing%20Cranberries.htm - suggests yields of 10lb from one mature bush.

Blueberries grown naturally in the UK too Urbanite!

My Blueberries have been very successful. Just need
picking alternate days and freezing in small pots.
I fed them with ericaceous liquid plant food every 6 weeks.
Thank you everyone. Will do some more researching.

They are on offer just now at Holland & Barratt, 2 for one.

Cranberries (there are a few species) are native to North America. The Eurasian species is known as the Cowberry or Lingonberry (Vaccinium vitis-idaea, syrup of which is sold in Ikea!).

Likewise the Blueberry (again several species) is North American whereas the smaller Bilberry (Vaccinium myrtillus) is our native equivalent that grows on hills and moors.

All are closely related and ericaceous.

Thank you everyone. Will look at my garden centre to see if they have Cowberry or Lingonberry. I have a spare large pot full of ericaceous compost.
All very interesting.
Am glad I asked.

They are known as Cranberry up here, Buddlejagar.

Lowbush cranbeery to be precise. But I think you will find the commercial varieties all hail from the Americas.

Oh and 'blue berries' are blaeberries to us!