Not too late at all - millions of things you can still sow (ok, maybe an overstatement) - but at the least
carrots, beetroot, kale,
then all the things that are best sown after midsummer - esp the oriental veggies (mizuna, pak choi, mustard greens, komatsuna and others), also fennel is best sown after midsummer, also swedes,
winter radishes are good
ongoing sowings of salads of course, summer vars of lettuce now, moving on to winter vars come the autumn
Do you know the Joy Larckom book Grow Your Own Vegetables - it has lists in the back of what you can sow every month throughout the year.
BTW I think probably a bit late for purple sprouting, I would sow a kale like Red Russian, you can still eat the shoots in the spring as you would PSB