@sport_billy I happened to be looking at the vets list and was quite shocked there was none close to East London so I am here with my own suggestion, just for other people that may need help. Hope that's okay!
A really good vet located in East London (in between Ilford and romford, in goodmayes) is Animal Ark.
The address and telephone number is below:
Animal ark veterinary centre
54 goodmayes avenue,
Goodmayes
Essex
IG3 8TW
02085888544
We have been using this place for about 20 years.
They have really good exotic pet vets there (quite a few of them) and they really really care about their patients. They see all types of animals there, I have seen a ferret and some really weird exotic rodent I have never heard of before, be treated there. I have a friend who's crazy about ferrets and she travels from quite a distance to go there because they just really know their stuff. They always answer any questions, squeeze you in if there's a problem, and they have another site around the corner that they use as a hospital wing.
My guinea pig Nine has been through it quite rough recently, and they have been exemplary and she's expected to make a full recovery (fingers crossed) , even after we were told before she went in for surgery that her chances were very low. And Zorro my other piggy, he had an issue (we now know to be just slight bloat!) and they wanted to be sure it wasn't anything too serious, and kept him in for observation overnight, just because they didn't want to misdiagnose him.
I have an ex teacher who has had guinea pigs for like 20+ years and I'm in contact with her as she works with my brother and she gives great advice and lives close to me and is always very supportive. The first day I got my piggies she asked me which vet I intended to use and said there was one closer to where we live. I explained I was going to use animal ark (purely out of loyalty and the fact my families pets have been going there for years, also because I suffer with terrible anxiety places I'm familiar with make me feel more comfortable) and she was absolutely chuffed with that choice too, when she lived closer to the goodmayes area they were her first choice too.
I can find out which vet she uses, and comment on this thread once I have the details, just for more options in East London.