Spring brassicas doing nothing?

Morning all.
Last October I bought some spring cabbage & cauli plants from B&Q,
brought them home & planted them same day in our small veg plot
in the space where the spuds had been, I even put a net over the top
of them because there was still some cabbage whites about. The ground
had growmore added to it after lifting spuds & was well trodden down
& left for a month ready for these plants going in.
My problem is that they have all grown well but that's it, no sign of any cauli
heads or cabbage hearts. Am I been to eager or is this down to this years
weather? I live in Rotherham & my brother who lives in Hastings planted his
spring cabbage a week before me (outside) started eating his at Christmas.
Any thoughts?
Keith 

yes around may early june