Professional Enquiries *cos we're good at what we do*

[Huguenot]

Is it a toilet overflow or roof tank overflow?

If so it's because the water is continuing to fill your cistern even though it's full up.

Either your ballcock/float is obstructed, or more likely either your filler valve is furred up or the rubber washer that seals it has perished.

Hopefully it's the latter, because it's relatively simple to fix - just turn off the filler pipe at the wall, flush the loo and unscrew the filler valve to expose the washer. If you take the washer into Dulwich DIY they'll almost certainly have a replacement.