[Rosie] I'll take a look at the valves when the window people have done their last and I've moved all the clutter back from the rad end to the window end of the bedroom. There's no TRV (which I think makes sense, as the boiler thermostat's in the same room) but also no "on-off" tap either as far as I know. There does appear to be something that can be turned with a spanner, so maybe that's the one to look at...
So while the new windows are great (or will be, once the final couple of panes are switched from single to double glazing), they have rather highlighted all the deficiencies in our central heating. Ho hum.