Also no one is saying everyone who claps is racist or a white, British nationalist. The actual question is whether the reason Captain Tom was so popular was because British society facilitates such figures (ie, white, respectable authority figure) and propels them to popularity under white. British nationalism.
Some people are too sensitive- A black man is critiquing society and offering his point of view and has to instantly retract it and defend himself. It reminds me of that Christmas advert where a bunch of white people got offended because it only showed a black family.
Black people are frequently discriminated against, suffer racism and adverse impacts, including poverty, discrimination in jobs and the workplace, etc, in comparison to white people, to name just a few. Recognising this doesn't invalidate white people or their existence, it is literally just an acknowledgement of the fact that racism exists and we as a society should do better to recognise this.