Interesting story, but quite ridiculous screenplay, and in an effort to be politically correct completely departs from reality. Police uniforms are wrong, Rose did not have a black husband - he was Irish, there were no black judges anywhere in the UK on 1920, let alone in West Sussex, and no black police officers. The storyline ignores the involvement of Scotland Yard and goes off in a tangent.
I suspect that Olivia Colman will sincerely regret her involvement in this disappointing farago of nonsense.
Not worth the effort of watching, you will never get your time back.