What winter bothersome bugs & critters do we have to contend with?

a lot depends on what happens over winter - if it turns out to be very mild, a lot of bugs just keep on going especially those that can take shelter from any sharp frosts ... whitefly in the brassica beds in particular don't seem to go away.  Having said that, if it is mild, I've even seen ladybirds around too.  And of course, there are the slugs ....

However, if it turns out cold with very hard frosts over long periods, the plants are more likely to suffer - they actually start to falter from lack of water, and frostbite can do some serious damage.  High winds can knock over stuff (make sure you firm in those brassicas to prevent them rocking) and heavy rains can turn beds into a swamp
 

PIDGEONS!!!
nightmare on my plot, i have to net onions and brassicas for most of the year