Kelsey Grammar's brit accent

He was supposed to be from Seatle. That is where Frasier was brought up because Martin was on the police force there all of his career. It stands to reason that the boys were brought up there as well. Where they were sent to school is another matter.
As for his "british accent", It wasn't really "british". There were just times when he was being hoity toity and affected an accent. He didn't always talk that way..... just when he wanted to impress. I found it silly. What was funny was when he talked naturally. It was as though he'd forgotten himself. He had!

i think you over thunk it.
I didnt even realise it was a british accent, and Im british!
I thought it was just an upper class american accent you might hear anywhere where the local accent is not too overpowering.
similar uncle Phil in "fresh prince"

It's just an upperclass American accent. Typically affected, but there are some wealthy families in the northeast who come by it more naturally, as their ancestors have been speaking that way for generations.

British accent???? I don't think so. He was born in the USA.

He was doing the stiff jawed, upper crusty Hahhvahhd accent.

It really makes no difference on the show, when you see the whole thing, as I just did. It's worth it.

It wasn't British at all. He was from Seattle that is why he moved back there.

Frasier had an uppity elitist accent that he might had borrowed from William Buckley. His mannerisms were from Jack Benny and some of his stick came from Bob Hope.

Many times in the show Niles or Frasier will pronounce a word the British way like when Niles once pronounced charade with the short a and Martin corrected him with a long a.

Fun fact: John Mahoney who played Marty was born and raised in England but Kelsey Grammer grew up in New Jersey and Florida