In the latest copy of Bird Table, the magazine for contributors to the BTO/RSPB Garden Birdwatch Scheme, Mike Toms writes that Wrens, Goldcrests and Long-tailed Tits all sometimes roost communally in nest boxes. (I'm doing this from memory, as I've lost the mag., which someone passed on to me.)
Might it be detremental to possible cosy roosting to clean them out at this point, considering the weather? Cleaning them I agree with to make them more likely to be used for breeding in spring, but maybe we should wait a few weeks.
(I'm not wussing out by the way, there's no place I love more than Hardcastle Crags in the snow!)
If we do go ahead, I can bring a 14ft. ladder, camera, bags and labels.