I think the other 2 dealerships where right and the dealer you went to was wrong. There is never any need to be rude to a customer ever(although if you lived in poland you wouldn't even bat an eye at it

) I think Honda UK should deal with this but at the moment they have your word against the dealer ( for the rudeness ) Go to the other dealer and get the work done there and don't use the original dealer again.
I would ask one thing, why didn't you ask to speak to the dealer principal about the rudeness or was he part of it?