Couple of things have happened.....
Thanks Claire for the input. (Couldn't call you Chopper!)
My Girlfriend (Miss Tramp!) owns her flat and it is the Landlady above who is causing problems.(She only owns the flat above us)
Keeping the thread updated for anyone who comes across it(Might help), we've spoke to our insurance company who have advised us that we should send a recorded delivery letter demanding that the leak is fixed and that we wish to have a timber specialist inspect the timbers. We are doing this.
Apparently in Scotland the split between flats occurs half way in the joists between flats. Our insurance company have told us that we should be able to prove negligence on her behalf and how to go about doing so.
We have been advised by our insurance company to write down and date everything that has happened, with even what was said during telephone calls written down. We have done this.
-The landlady upstairs has admitted on the phone that the extractor fan in the bathroom has been disconnected for some time.
-That she has been aware of a damp smell in the bathroom for some time.
-We also have photos in behind the bath showing quite clearly the mould and fungus growing on her floor and the rotting floor boards. (Note to do this we asked the current tenants if "it would be possible to take photographs for our insurance company") This was a great move and the current tenants were only too happy to let us in to to this

-the current tenants have stated that she never maintains or checks the flat
The insurance company have stated that if she doesn't satisfy us within our allowed timescale (we chose 7 days) their legal department would take over for us. Not bad for us so far.
So it's looking good.
I'll tell my tale on here for anyone else who needs in future.
DT