I always appreciate knowing the outcome of the cockerel/pullet debates in these threads, so wanted to update that
@fleurchickens was quite right - our late July hatch were all cockerels, every last one.
Fate has a way of intervening and it turned out one of the chicks took sick for a couple of days, so I pulled momma hen out (much to her relief - she probably knew they were all boys for weeks!) - she settled back into the main flock okay.
The rowdy cockerels are still in their separate pen and I'm glad we never bothered to integrate them as I think it would have created more stress for the flock, who would only have to adjust again when we rehome the chicks - hopefully in the next week as there is a LOT of crowing coming from the little coop in the morning!