I returned from a 6 week stay in South Africa yesterday (currently self isolating for 10 days), and I made damned sure that I followed all the rules, regulations, certificates and sworn declarations that were needed to leave South Africa, to enter France and to enter the UK.
And yet, both at Johannesburg and CDG airports in Paris, I saw passengers arguing the toss with airline and security staff that they didn't have the correct documentations but insisted they should be allowed to fly.
Moreover, on both planes I saw some passengers removing their masks and arguing with the stewards and other passengers.
What happened to them when they reached T2 at Heathrow I really don't know (a fine perhaps?) But both flights were extremely stressful because of their idiotic attitudes and lack of following requirements in terms of documentation.