A great evening with my lovely niece watching Seth Lakeman https://www.sethlakeman.co.uk/
I am not musical but fascinated by the instruments being played.
Maybe someone could tell me what the box is.
I would say it is some kind of squeezebox or accordion. That must have been a fabulous evening, he is reputedly a fabulous musician and entertainer. Love the shot. Full of anticipation.
I agree with Casablanca and Babs that it's a type of accordion or squeezebox