Brassicas (cabbages, kale, broccoli etc) are well known for being on the receiving end of pest damage, and whilst many pests are less of a problem now, you should still protect your autumn brassicas.
Cabbage White Butterflies are still active, and laying eggs, although not for much longer now – a sheet of horticultural fleece laid over the top of young plants should keep them protected for the next couple of weeks. Or if you are protecting them from pigeons as well (see below) then use an insect proof mesh net to keep both butterflies and pigeons out.
Pigeons are a threat to brassicas all year round, so if they are regular visitors to your garden/plot, then it is sensible to protect any autumn growing brassicas right through till harvest. We’d recommend making a hoop frame to support netting to keep them out, or you can prop up a net with bamboo canes topped with upturned jars. Use an insect proof mesh net which is less likely to entangle garden birds, and also keeps butterflies out.
Slugs and snails are still active, so definitely protect brassica seedlings from these, as well as protecting your other autumn/winter crops, especially during wet spells like this one.
Cabbage Root Fly is not a real problem at this time of year, and the season doesn’t start again until April, so for the most part you won’t need to worry about this for autumn/winter brassicas.
Club Root is usually only a problem while the soil is warm, so just be vigilant for a few weeks until the temperatures drop. Check for signs of wilting or stunted growth. If you have healthy soil with plenty of organic matter added, it is unlikely to be a problem.