My personal belief is that the regulations are nothing to do with wild bird nor domestic flock health. One aspect is the government covering their backsides against compensation claims if they did nothing and poultry keepers suffered large losses. But by far the most important aspect, and the reason for the emphasis on poultry, pigs and waterfowl, is the risk of the virus multiplying, mutating and becoming pathogenic to humans, which, history tells us, is most likely in poultry, waterfowl and pigs.
So little backyard flocks are probably very low risk, as is cross contamination with wild birds in back gardens. Not no risk, though, and there is still the issue of the impact on your neighbours if a case were to occur.