Third, the threat to make the UK tax havens comply is in itself significant. It challenges one of the long held but wholly untrue claims of these places that they are independent locations that can legislate for themselves. In practice they can legislate but only with the consent of Westminster. In that sense they are like Northern Ireland, Wales and Scotland at present, all of which legislate in parliaments whose existence is subject to Westminster consent. And that consent can be withdrawn: the ending of Stormont rule on occasion and the UK walking into and taking over rule of the Turks & Caicos Islands is evidence of that. The imposition of law on these places, which cannot pass any law in any case without the consent of the UK, is entirely possible.
Well, no. Some are Crown Dependencies, where internal law is a matter for the Queen as Duke of Normandy (at least, as the remnants of the Duchy) some are colonies (Anguilla) some are dependencies (say, Turks and Caicos) and some are fully independent countries. Those last don’t have to consult London on anything at all. To argue that they do is colonialism of course.