I have found my backseat in my ba falcon collecting water, i have removed it and found a bung on the left side. It is not easily removed any chance this could be where the water is coming from? It seems the most logical explanation as it is the only wet place. Can i remove this without damaging it? Any ideas how to stop this 'leak'?

I'm assuming that the bung is under the seat, so it's unlikely to be the problem. You also say it's hard to move, so again unlikely to be the leak. You could pour some water into the area the bung is supposed to drain and see if it leaks out, if not then it's sealed and deffo not the problem.

As to where it may be coming from, buggered if I can help.

I think you will find the leak is coming from where the boot water chanel runs under the rear window and the water is running down behind the rear seat..
seen it on a few ba bfs

Ah so it is. Problem fixed now appreciate the help