London has a number of great places to acquire vinyl.
Number one is probably Grooves, right downtown. Their new pressings collection has been expanding greatly.
https://groovesrecordstore.com/
Second would probably be The Village Idiot, in Wortley Village. Huge collection, mostly used.
https://www.facebook.com/TheVillageIdiotWortley/
There is a huge antique store a short walk from my house, which has many rooms of items sold on consignment. I pick up 3-4 albums per month. Often for a steal (they have everything, including wax cylinders, shellac 78 RPMs, giant amount of big band/jazz, and seventies cheeze.)
LFP