Kevin,
"It is nonsense to suggest any criticism of anyone Jewish for anything whatsoever is antisemitic."

Yes it is nonsense.

I suspect that the Board of Deputies of British Jews has as much reason to be taken as representing the views of all British Jews as the Muslim Council of Britain has of representing the views of all British Muslims.

They are unelected. In 2016 a survey done by Policy Exchange found that about 2% of British Muslims felt that MCB represented them.

Jim,
They can only be described as "representing" anybody if they are an elected body - they are not

Yes they are.
The Board receives Deputies elected by individual synagogues, confederations of synagogues, and other organisations within the Jewish community such as charities and youth groups.