Can I buy foie gras in the UK?

Yes, it's available to buy - not cheap. You'd probably need to shop in upmarket food stores / ask a butcher if they can supply

You're not actually missing out by not trying it.  I have in a past life eaten very high end foie gras and it does not taste any better than a high end goose liver paté.  The difference is in texture - it's fattier, and to my mine not in a good way.  It's not unlike biting into butter.  If you've ever bitten straight into a block of butter and ever tried goose liver paté you can exactly imagine what it's like if you have any imagination at all.  There are fake foie gras out there where the texture is imitated by adding goose fat but I honestly don't know why people bother.  Humans discovered that goose and duck livers were especially delicious in the autumn because the birds cram themselves in preparation for winter.  Then we got greedy and cruel and started force-cramming beyond their natural capacity.  If you look around you can buy "natural feeding" foie gras, where the birds feed themselves as a natural response to autumn.  It will most likely originate from Spain.  It is not quite as fatty as force-crammed goose, which I prefer leaving aside ethical considerations, but the flavour is every bit as good, which is something you can't say for the "faux foie" where the liver gets diluted by the general goose fat.

You do understand that the duck is FORCE FED in a cage for its entire life, never once walking or actually living - " I know how it is produced". You want me to tell you how to support that abuse. Oh, c'mon, it's just one time. Yep, and so too have millions of others heard the marketing and are curious. Just once, millions of times over. 

Will I support the intentional and lifelong abuse of an animal? Nope. Do I eat hamburger? Yep and it is locally raised and humanely(quick and immediate) killed. The same goes for the rest of the meat I buy. When I walk onto the those farms/co-ops I'm not left with a guessing game how my meat is sourced and how the animals are treated. But this kid over hear wants me to be nice and abuse animals for his culinary pleasure. Idiot.