Thanks for the replies. I will investigate further by putting plug in and monitoring. What also concerns me is that the wall has got mould on in the area where the pipes would be so it raised my suspicions.
In our kitchen when we put the taps on I can hear a dripping sound coming from behind the wall where I expect the pipes bring the water from upstairs. I therefore suspect one of them is leaking. a) would it involve ripping out plaster from wall to get to pipes? or b) would these pipes be...