Gggrrrrrr! A couple of my sprouting broccoli are bolting Where they start the rest are sure to flower. If it's getting hot with you, mulch around the roots.
I have found if I cut off every flower, and every lot of buds about to burst, i can sometimes bring them back.
Am leaving one of mine to flower at the moment though, as it seems to be providing the bees with food - middle of winter here, so flowers are a bit scarce.