I have read an explanation of people who spoke yesterday. Seemingly, Ed Davey is allowed to speak at 1 in 6 PMQs and this week was his turn. There is also the SNP etc so there wasn't enough time, and, as you said, Dianne Abbott, is an Independent. It's run on party lines, not subject matter...
I just looked it up. Throughout the run of the play, there were just two nights where black people were invited to attend 17th July and 17th September, all the other nights were available to anyone, but even on those nights, nobody would be turned away. It was about slavery.
To be honest...
There are many support groups within the police forces. Black, Jewish, Women, Pagan, Muslim, Disabled etc Is that a problem?
https://www.joiningthepolice.co.uk/supporting-diversity/support-organisations