There is i believe a responsibility of dog owners to act reasonably in ensuring their pets do not disturb protected species.
Certainly when it comes to badgers it is the sett , the badger and even the access areas that have protection.
In the case of birds, it is certainly an offence to disturb an active nest, which includes one that not only contains chicks but also, eggs or in fact during laying.
Interestingly as an aside, once a wild animal becomes captive (under the dominion of man) it is effectivley afforded the same protection as say your pet dog. So one wonders if you confine a wild animal and restrict its movement by fencing it in ...is it then under dominion..?? This would also apply to a grey squirrel that was trapped and kept so for a period with knowledge of such before dispatch, i say this because i once had dealings with a guy who caught one and decided to go shopping before dispatching it.
In my view dogs should always be kept under control, we only have to look at recent reports to see the problems they can cause. i love dogs but in my experience a significant number of owners cannot recall their animals and if they cant command them they shouldnt be off in the first place. I dealt with an incident only yesterday where a dog on a footpath through a field had run off terrorised the cows and calves (plus a bull) and one had carreered into barbed wire and ripped its flank open...when will people wake up.