rude-stuff
Which would lead british pilots still with just a british license. Based on nationality there is a case to be made for EU citizens, as i posted several times above. They were disadvantaged, though with ample, very clear and precise, three years of warning by EASA. British pilots and british resident pilots are not disadvantaged, they still hold a british license.
And of course, you completely dismiss the element of oversight, which is crucial to any safety sensitive area.
That said, there was a clear advise from EASA to switch to EASA licenses as early as possible. And everyone could start that process until the end of last year where EASA oversight was still present. There is a clear reason why bigger players like the orange bunch switched their continental crews to non-UK licenses (more than two years ago already), and supposedly even quite a few UK based trainers as well. All based on publicly available advise. In the end, there will always be some who miss out on a deadline issue, but judging from the number of posters on this thread compared to the many SOLI threads, it is actually quite a small number.
Of course one can try a legal case, which, in any case, will take at least 3 to 5 years, a time probable better spent on just getting on with it and regaining the license the "normal" way if one needs it right now.