Thanks for heads up guys. I got the new door and targa rubber today so fitted them. Poured water over the roof and hey presto no drips on the seat so that's one job done, but noticed water p**sing into the drivers footwell via my fuse box again. Took it all apart and found it was indeed the targa pipe that had disconnected from the tube that takes the water out near the wing, so it was pouring into the car instead.
It was a hell of a job to get it back, the tube had shrunk (I assume with age) and no amount of pulling got is near the outlet pipe. I ended up cutting some of the outlet pipe and using this to connect an extension to the tube. Anyway, a bit of a Heath Robinson job, but it works and no more water leaking into the fuse box. I now have the carpet up and the dehumidifier running in the car.
So thanks once again, it would've taken ages to find the problem without the pointers.
Gaz