Range from the cheapest unblocking of a clogged toilet £70 (RR'S Builders based in SE12) to the dearest unblocking of a clogged toilet £180 (Dulwich Plumber based in SE13).
Comparing plumbers estimates for a blocked toilet 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 unblock a toilet in SE8 by posting a job with HaMuch and we will send it to plumbers in SE8.

"Unblock a clogged toilet, bowl almost full. Ideally today or tomorrow service."
SE4
"Blocked toilet (not overflowing) - have attempted to drain with drain snake / auger and haven't managed to remove blockage. Time sensitive problem issue and we would need to have it resolved in next 24-36 hours."
E14