Yup.So thats not the reason for these havens. The reason is to avoid tax altogether.
Alright I may be wrong about this but here's what I think about this. If David Cameron's father set up a tax fund for international investors in a tax haven, that seems perfectly reasonable to me. After all, if you're a US resident, you pay tax on the profits you receive from that fund the instant they enter the US, right? Same with the UK (I presume). And the same for most people in most countries in the world.
So if you set up that investment fund in the UK, as an investor, you'd pay tax on the profit derived while in the UK, and then more tax once those profits land in whatever country you reside. So you'd be paying two lots of tax. So it makes perfect sense to me to set these funds up in jurisdictions that have very low or no taxes at all - because unless you reside in one of these jurisdictions, at some point, the money you've made from that fund will be taxed.
So if I've got that right, what's the big deal with people doing things like that? Obviously if they're sneaking money out of the country in a mattress in the back of an old XJ400, that's well dodgy. But if they're just availing themselves of a means to not be taxed twice, I don't see the issue - as long as when the money finally arrives at their home, they pay the correct amount of tax there.