I'll do my best to explain what's happening.
We've started to get a lot of water leakage when draining the bath. I've had a look around the trap and the waste pipe and it appear like the seal, or whatever it may be called, between the underside of the plug and the waste pipe/plug outlet has failed.
I'm not sure if waste pipe is the right description or not, it's basically a molded black piece of plastic that is connected directly to the underside of the plughole/bath and then connects to the trap.
On closer inspection, and what suggests to my simple brain that it's the root casue, I can see play from side/side and even up/down - the up/down movement is still quite small, about 1-2mm, but I'm guessing that is more than enough to see the leak that I'm getting.
I've still tried a few test runs i.e. drying all of the fitting under the bath with tissue and then running some water down the plug, each time it's the black plastic waste pipe that gets wet first. I can't see any leak coming from any of the nuts around the trap, they only appear to get wet once the water starts running down the outside of the waste pipe.
The black waste pipe itself appears fine, it's just the seal/washer/join/whatever between it and the bottom of the bath/plug hole. Any tips are very welcome!