I think I have the answer, thanks to the handyman at work. He sayes its water overflowing from the toilet cisten, which makes sense as water seems to be constantly moving in there.
thats correct - its the overflow hole on the bath. I will give the drainage test another go (although had not notice any drainage conerns. re the shower thought have to admit I dont know how the water diverts. i know their is a pump for it it what was the airing cupboard (until i had a new boiler). ...
