I found it quite difficult in my area (North - rural area). There are two or three vet practices not far away but finding someone who knows about hamsters isn't that easy. Nearly all vets with a small animal department will treat hamsters but aren't that expert in them usually. "Small animals" tends to mean cats and dogs "Exotics" tends to mean other small pets like hamsters, guinea pigs, lizards, rabbits etc.
I don't think there are many actual "exotic" vets in the Uk - few and far between anyway.
What I tend to to do is look up a practice's website - see if they have any info on hamster care at all (I found most don't) and if they do, see how correct it is! Then I look at the list of vets and their specialities. If you can see one that specialises in "small furries" or has a guinea pig, rabbit or hamster themselves - then go with that one - and ask for that specific vet.
I tried the finder Drago linked but it only linked two in my area so maybe a local search would be better.
I had a look on Google. The nearest proper exotic vet I could find (and they do specialise in hamsters and other "exotic" pets - is in Bedford - a bit of a trek probably - about 65 miles.
https://www.scottveterinaryclinic.co.uk/exotic-pets
What you might be able to do is register with a good general vet nearer to home and then ask for a referral to the one in Bedford if there is anything serious needs treating (hopefully not
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I can't see any vets in the Windsor area that even mention small furries or hamsters in their specialisms, but this vet practice looks like a good general one with a few vets specialising in acupuncture as well. You could ring them and ask if anyone specialises in small furries or hamsters.
Vets at Alma Veterinary Hospital | Windsor | Berkshire
There's this one in Maidenhead (about 20 mins?)
The last vet on the list is an exotic vet with an interest in small furries
Veterinary Surgeons Archives | Pines Veterinary Clinic
This is a general vet in your area that sounds good - has lots of testimonials including from owners of ferrets, mice and rats.
Kelperland Vets | Vet Services Slough, Maidenhead, Bracknell, Berkshire
I think the attitude of the staff in the practice is important as well as their specialisms. Having had the experience of dealing with one vet who wasn't very compassionate!