The logic of this tweet seems to go along the lines of: "it's OK to have some non white people on #NMUKITVGMB - in a tokenistic kind of way (because after all, it's not like they're essential of anything) - as a type of 'decoration' / evidence used to stave off criticism of being racist, but of course, because they're not fulfilling an essential role - the more of 'them' i.e. #MetaphorVersusUsThem that you have the fewer 'legitimate' i.e. white people that you have to do the actual job". The 'give away' is the characterisation of a "British white person" i.e. a 'legitimate British person' (pointing to the idea that #IdentityWhite is an essential attribute of Britishness). The tweet is an overt example of deep-seated #OtheringDiscriminationRacism and strongly implies that the author feels under attack i.e. #TheoryPoliticsOfFearAnxietyOfVictimisation as they struggle (resist) to engaged with contemporary society i.e. a #TheoryPoliticsOfEternity if ever there was one.
Interestingly, the image used to illustrate the tweet is taken from a video, which shows #OrgClassifPPUKConservativesBorisJohnson, moments before being infamously stuck on a zip-wire while intending to celebrate/raise awareness for the UK winning its first Olympic gold medal in the #2012_LondonOlympicGames i.e. an image that has become synonymous with #TauntSnatchingDefeatFromTheJawsOfVictory i.e. https://www.theguardian.com/politics/2012/aug/01/boris-johnson-zip-wire Presumably, the image is meant to signify a sense of #PoliticsNationalismConservative re #TauntFlagWaving etc.
Supplementary: #2006_Borat version of infamous image: https://www.toonpool.com/cartoons/BORIS%20BORAT%20JOHNSON_343996