Nice advice here, but let’s just be clear on use of the words ‘sow’ and ‘plant’: Ness I presume you mean plant when you say plant?! eg four week old plants? Just because I would plant PSB and kale in August but find that too late for sowing it.
And yes Adrienne you certainly can sow PSB now and I am about to myself, it can still grow quite large. There is a slight possibility that April sowings are more frost hardy (Darren’s comment here) but my June sown broccoli gave wonderful harvests this spring and grew big too.
Also you can module-sow swede now for planting after early peas, beans and salad.