Box Springs?

We left our king size mattress in the US on the assumption that it would be a tight fit for most UK bedrooms.  I'm shopping for a new mattress now, and it strikes me as odd that I see no adds on line for box springs, just for mattresses.

What am I missing?   Do the British just not use box springs, or do you buy them in a special store?

You don't really see separate box springs here.  Instead, you'll see 'divan' beds, which are basically beds with built-in box springs. 

Aha!   I had seen ads for divan beds, but since my prior association with the word "divan" was "couch", I thought those were day beds.  :-)

Thanks for the help.