Low flow from cold taps?

I have a meagre flow of water from the cold taps in the bathroom and cloakroom. The cold tap in the kitchen has a good flow. The problem occurred after a plumber had to repair a leak in a kitchen pipe run, which he did by inserting a short new length of pipe. This run also feeds a water softener with isolating stopcocks, but these appear to be fully open. Any suggestions?