Direct Sowing in August
There are still quite a few things you should be sowing in August. Spring Cabbage and Chinese cabbage, which is a late crop as well as hardy lettuce.
Although we think of lettuce as a summer crop, it is a surprisingly hardy plant and under cloche and in the greenhouse can easily be available for a Boxing day salad rather than some tasteless import from sunnier climes.
Sow spring onions like White Lisbon winter hardy which will grow, albeit slowly, to add zing to that salad along with some fast growing radishes.
Late spinach can be sown in August along with a last sowing of kohlrabi and turnips.
Planting Out in August
Plant out the savoy cabbages and cauliflowers to grow on for the earliest crop as well as hardy kales.