Poland won’t be able to stop British riders plying their trade in Britain. Unless they are employed full time, the riders are self employed and it would be a restriction of trade. Would never stand up in court.
the Polish league could say we are not going to employ these riders who refuse to obey us, but again that would be discrimination. And would Polish clubs tow the line when there are British riders they would want in their team?
They could test the waters but Kurtz, Holder, Doyle and a few others could refuse the rule or demand a large wage rise which covers their loss of earnings.