The diversity figures for historical shows is far higher than the population, of say Downton Abbey's setting. It requires a lie.
Stuff set in modern day also require a far higher portion of ethnic and racial minorities than we see in the UK population. Even a show set in an all boys school (think opposite of FACTS OF LIFE) would need to have half the main cast be female.
Firstly, it would need to meet that criteria only if it wanted to be considered for a BAFTA. It doesn't 'have to' do anything.
Secondly, to repeat my first point, the specific diversity of cast requirement is one of 4 standards. To qualify, a show has to meet 2 of those standards. If you're really so precious about how accurate the historical race or gender representation is in your BAFTA nominees, fear not! They can qualify by meeting 2 of the other standards.
Regardless of which of the 4 categories you look at, it's based on anti white discrimination, because it doesn't reflect the UK population, as it claims.
I can't find a single post, thread, mention, even slight nod or a wink that suggests these diversity targets are supposed to reflect the make up of the UK population. It does say it attempts to encourage those in the industry to be more inclusive and representative - though it does NOT say that it should represent the racial or gender make-up of the UK. As for discrimination of white people in the film or TV industry, i think you'll be hard pressed to find evidence to support that claim. I've certainly never heard it mentioned.
Its like how BEING HUMAN had to be recast, even though the pilot episode was a hit, because it ran afoul of the diversity rule for the BBC. It's nearly impossible to find the original pilot episode because it wasn't diverse enough.
I can't speak for the pilot, but after watching the re-cast version (though its been a while), It turned out great. I understand you might like the previous version better but i'd argue your particular view on the matter might be interfering with your enjoyment of a genuinely funny show, though if i remember rightly it went down hill after a season or 2.