We have a robin who’s been coming into our gardens and home for several weeks now. I am concerned as he seems unable to close his beak and now appears to be finding eating difficult. Can you advise. Thank you

Am afraid not much can be done with wild garden birds if they are sick or injured...usually best to let nature take its course....
I have provided a link below which should hopefully advice you on some diseases and illnesses birds are susceptible to and also advice on what to do regarding feeding.

www.rspb.org.uk/.../

Sorry I can't give you ant better advice ...perhaps someone more knowledgeable than me can offer an alternative

Just seen this post today.
Possibly Trichomonosis (canker)
Quite common in caged and wild birds .
There is loads of info on the internet about this disease that covers a multitude of symptoms especially the symptoms you have mentioned.
And there are vetinary organisations that will treat the illness especially in caged birds .