I’m not a lawyer but own a number of shares in a number of companies through IG in the UK. Since you don’t really own the shares, the broker (in my case IG) hold them on my behalf in a ledger that simply allocates the shares to me then I imagine they can do what they like with the shares. So long as the money is there when you want to liquidate it then it’s irrelevant to some degree. In the UK the value of the shares…
I assume it is still the same in the UK post-brexit, but I have not looked it up.