It's always funny when Brits complain about foreign tax havens. The UK is a massive tax haven, with oodles of little overseas territories, or Isle of Man, or the Channel Islands.
Urgh. This is part of the problem. They're Crown Dependencies. They're neither fully independent countries nor part of the UK. They're accountable to their own local electorates but host a lot of firms doing business that's really in other countries. They're ideal tax havens.
I am fond of the constitutional tweeness of Man, Sark, etc, but their situation really does need to be regularised.