So... Looks like an airlock. I turned all the offending taps on full and after a couple of minutes slower flow and some spluttering the 'seem' to be back to normal service
Further investigation: the downstairs loo basin cold is also slow. The slow ones all seem to be fed from the same exit pipe from the cold tank. No obvious blockages going into the outlet, though, and as I say it's happened all at once, not gradually :(
OK, I just went to have a shower and nearly burnt myself because hardly any cold is coming out there too. So it looks like it is all upstairs cold water...
2x bathrooms upstairs. Both basin cold taps suddenly running very slow. Bathroom hot taps run OK, bath cold tap runs OK (maybe a bit slow), all downstairs taps fine.
I checked the cold water tank in the loft and the water level is nearly up to the top.
Any ideas? what is weird is that it has...