Hi Sammy
I too am from England, and don't have a car, and live in rural Suffolk. I recently adopted two rescue pigs. I just wanted to reply to a point you made about the the service rescues provide in the States to take guinea pigs to their new owners not being available in the UK. I have found this to not be the case at all. Many of the UK's rescues rehome nationally, many will set up 'piggie trains' to get pigs across the country to their new home, and most rescues will be happy to travel some distance to do home checks and rehome.
You don't say where you are in the UK, but there are rescues in most counties. You may have to hunt a bit to find them, but if you look on
GUINEAPIGREHOME.CO.UK you will find a pretty long list. If there isn't someone in your county, then try contacting the closest rescue, they will probably know of someone closer to you, or if not then are probably used to rehoming in your county anyway. You can also try the RSPCA, which will have usually several branches in each county.
Not sure if I'm allowed to post a link to another forum, but there are a couple of very helpful UK based guinea pig forums that have a strong rescue ethos, and have lots of contacts for finding lovely rescue pigs, (I find it hard to resist those that appear on the sites!), do a search on google and I'm sure you will find them, or PM me.
Anyway, I'm new here too, and don't want to enter into debates about pet shops, but I just wanted to make sure you were aware of the rescue options next time. Good luck!