Ewan, since the pipework is all connected, the *pressure* must be the same throughout-it is the *flow* with which you are presumably having problems. The most likely cause is some sort of restriction-perhaps pipework that is almost kinked, or a partial blockage at the tap (you did not mention both taps). Its possible the tap washer is breaking up and part is lodged? I think I would disconnect the feed to the affected tap-if you get a good flow then its the tap, if not you'll have to work your way back along the feed to find the problem