It's not a fun job but someone has to do it...

Stop flushing it and turn off the water supply. Bail out as much water as you can with a bucket. Get the plunger out and place the rubber end over the hole at the bottom of the toilet, and pump the handle up and downwards as if your life depended on it, creating suction in the pipe. This usually fixes the problem, just remember, don't flush whatever has appeared without breaking it up first. I know it's grim but you could just block it up again...

No luck? Get the drain un-blocker and squirt it down the bottom of the bog into the u-bend, and leave it for as long as it says on the bottle. This can help break it up a bit, once done flush it and see what happens...

The mains water valve could be anywhere in your house, so hunt around. More common locations include above or around the front door, in utility rooms and near boilers.

If the evil deed is still offending then it's time for the thin hosing... it needs to be long and bendy but tough, like very flexible garden hose, or hosing from a local hardware shop. Basically shove the hose down the toilet and try to get it round the bend to break up the blockage. Don't be too aggressive but work at it to get it right round. If you still find it is blocked then it could be a messy job, so probably best to get a professional in.

For more complex repairs and plumbing work, we say - call in the professionals!