if there is no written sign about breeding birds and asking for dogs to be kept on leads then ignore him. I can not see the police getting involved.
The man himself wants to watch what he is doing. the police do not taken lightly gun owners who show aggression regardless of whether they are carrying a gun or not .
I dont think this is strictly true Lorna, sorry.
If the chap has Permission he will be rightly upset if nesting birds are being disturbed as they will abandon nests/young.
It is nesting season and we should all be mindful where we let our dogs roam plus have dogs under control on lead or off. If you are able to demonstrate a reliable stop, also recall, you may find the “man who owns a gun but not with him” may be a little more relaxed about your dog having a run. Are you keeping to the footpath? and that means up to 2m either side (including your dog!) Do you know what the field is used for? Is it a young crop and damage may be done to yield?
We have Permission on the land behind our house. This time of year we dont go on to it, even though there is a foot path and we have explicit permission to use the whole field! Its full of wild flowers, grass seeds, small animals and nesting birds including pheasants!
Whilst the field looks “unused” he is paid to leave it alone as its classed a wild flower meadow. (Dreadful for hayfever!).
Chasing is a dog out of control. Most songbirds are protected in the UK so I don’t understand why you would allow your dog to chase them. Chasing rabbits is also bad form and may well be the Permission the man is getting upset about.
I’m sure this isnt what you want to read but I would suggest teaching your dog not to chase so you can both enjoy your time outside and be able to demonstrate he is under control!