faulty bathroom mixer tap?

[jamie2013]

Hi, I'm in the process of having a new bathroom fitted and having a bit of a dispute with the fitter. He's fitted a mixer tap on the bath and on the basin. Both from the same range, the one on the bath is the sort that requires 2 holes on the bath and the tap on the sink the sort that just need one (sure there's a technical name, but I'm no plumber) . Anyway, the tap on the bath works great, a nice steady flow, decent pressure etc. The tap on the basin though, yes not much more than a trickle, it splutters and isn't a steady flow. The fitter reckons that that S how is supposed to be and is refusing to change it or fix it. Does anyone know what might be wrong with it?