Remember, as I've often said before, always sow the seeds. You can catch up on everything else, but if you don't sow seeds on time - you've often lost your chance. This is especially important for late autumn and winter crops!
*Also Important* - If you haven't got seeds of some winter vegetables you will need then get them as soon as possible, as many garden centre shops take their seed displays down this month, and online may also be sold out.
Seeds to sow outdoors for autumn and overwinter crops:
In modules, in a seedbed for transplanting, or in situ where they are to crop: beetroot, brocoletto 'Cima di Rapa', carrots, cabbages ('Greyhound' and leafy non-hearting spring types**), overwintering spring-heading cauliflowers**, peas* (early dwarf vars.only now), Florence fennel, 'Witloof' chicory (for winter forcing), sugar loaf chicory, radicchios, endives, salad onions, claytonia, landcress, lettuces (Lattughino, Fristina, Winter Density, Jack Ice, Cherokee, all good varieties), kohl rabi, 'Hungry Gap' kale (for spring cropping), radishes, rocket, Swiss chards and leaf beets, perpetual and summer spinach, summer white or yellow turnips, Chinese cabbage, Choy Sum, Pak choi, mizuna, mustard 'Red Frills' and other oriental leaves, Chinese kale (Kailaan), lamb's lettuce (corn salad), salad mixes, herbs such as parsley, chervil, coriander, dill, fennel, buckler-leaved and French sorrel. Also sow some single, quick growing, annual flowers such as limnanthes (poached egg flower), calendula, Californian poppies, nasturtiums, phacelia, etc. to attract beneficial insects like hover flies to help with pest control, and bees to help with crop pollination. Sow fast growing green manures like buckwheat, red clover, mustard (which is a brassica so watch rotations) and Phacelia, to improve the soil, 'lock-up' carbon and feed worms (after digging in), on any empty patches of ground cleared of early crops that won't be used for 6 weeks or so, or which needs improving. This is also the best time of year to sow all types hardy herbaceous perennials, biennials and wildflowers. Foxgloves, primulas and hellebores in particular germinate really quickly and easily if sown as soon as this year's seed is ripe.
Again - sowing into modules means that you will get maximum crops out of your space by always having something ready to plant wherever there is room - bigger module-raised plants are also more resistant to slugs etc! Sowing a wildflower meadow mix in seed trays or modules is actually a far more reliable method of establishing a meadow than trying to sow directly into grass where there is too much competition from other mature plants and also many pests. These can be planted out in patches later.
(*Early July only, ** mid-late July)