I have 6 blackrocks and a few of the guys in the allotments around me have quite a few as well, they're great birds, cheeky little characters and great layers. Mine have been laying all through the winter including through the bad snow we've had ,they seem to love being out in bad weather.
They are far better layers than my Rhode Islands or Welsummers, I intend to get a few white leghorn chicks when the weather warms up, to see if they are as good at laying as people say!