Range from the cheapest replacement of a toilet float valve £25 (MJM Plumbing & Property Maintenance based in SW1V) to the dearest replacement of a float valve £85 (LUCO - London Utility Company based in W1W).
Comparing plumbers estimates for replacing a toilet float valve in the cistern tank gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
What to do - Get rates and quotes to replace a toilet float valve in Regent Street by posting a job with HaMuch and we will send it to plumbers in Regent Street.

"Toilet in basement no longer refills, so won't flush. I believe the issue to be an internal fill valve issue or blockage. The pipe goes behind drywall so hard to identify the exact fault. Just looking for quote at this stage. "
W1S
"Replace float valve in toilet cistern"
LONDON