We had a similar issue a few months ago. It turned out to be a knackered washer in one of the pipes leading to the cistern. The leak was that slow you couldn't see it dripping, put the pipe was wet there it was trickling down.

Okay, ignoring the OT stuff, I managed to see a drop fall from the underside ofthe cistern. It's from the same corner as the puddle. I don't know if it's from the outflow pipe connecting to the cistern or from where the flush pipe connects to the cistern.

An indicator and short term interim solution would be to tie string around each of the pipes you have mentioned where they meet the cistern. Make sure they are tight around the pipe and long enough to almost reach the floor. Firstly whichever string gets wet identifies the culprit junction. Secondly if you put the tail end of the strings into a bowl or large mug then capillarity will capture the water.

Kitchen roll shouldn't be flushed.

No I think it has missed the pan.

3 things come to mind....

1..... a leak from the water inlet gasket.

2.... overflow pipe leak.

3.... condensation.

If the toilet is in the same room as a bath or shower I'd go for number 3.

Numbers 1 and 2 should be fairliy easily sorted too.

Good luck !

Toilet is in same room as shower and has been for thirty years. I wondered if it was condensation too but the problem has only shown itself now, and not, say in cooler climes.

I plan to stick some Bloo into the cistern and hopefully it'll leave a trail.

I had a feel with some toilet roll and there was moisture on the underside of the cistern as well as one side (same side as puddle).

I would still put a lock on the door or a CCTV to check that it is not a tramp.

There's a tramp round here who has been known to let himself into peoples' houses to raid their fridge and whatever else - mind how you go

I hope so, especially if it's a leak from the soil pipe.

Toilets deal with numbers 1 and 2 quite effectively number3 however is outside its normal operating parameters.

The ballvalve diaphragm will wear over time. The consequence of this is that the water level in the cistern rises. If the joint for the overflow is badly seated it is of no consequence until this time. Replace the diaphragm and if you want to, re-seat the overflow outlet.
With that design of loo the most frequent problems are with the flush pipe though.

Okay so I yanked off the lid of the cistern. After a flush, the water refills about half-way up the overflow pipe! Consequently, there's water leaking through a plugged hole in the cistern. This hole is where a toilet handle could be placed (it's on the opposite side).

Can't detect any leaks around the inlet/overflow pipes.

There's been a lot of water recently and part of it is probably due to condensation - it's improved since we've made sure the window is always open.

I've adjusted the screw on the balloon valve thing and made sure the water level is about an inch below the overflow pipe. We've flushed the toilet five times since and there's no leakage whatsoever.

Fingers crossed it stays like that.

Sounds like that man sorted it !

Well done.

Taking the lid off and having a look is often a good start to solving the problem. I bet it took you longer to do the diagrams

That's what my mate the brain surgeon always says