n3dsd you jumped the gun there mate
First paragraph states I'm aware it's not illegal!
No, he didn't jump the gun. Tax EVASION is illegal, tax AVOIDANCE is not. You referred to tax evasion as if it were what Cameron has done and also as if it were legal. Evasion means a false pretence about what you earn so that you do not attract tax, avoidance means truly declaring your earnings but using legal structures , allowances and expenses to offset the amount of tax.
2015 tory manifesto. Crack down on (aggressive) tax avoidance. It's there, all written down. The Tories responding to schemes like K2, criticising Starbucks, Apple, Amazon etc but then quite happy to have done much the same avoidance themselves.
You could argue that a fund that is administered from the UK and is setup in a tax free jurisdiction is aggressive. It's being done with the primary motive of avoiding UK tax (most likely corporation / dividend tax) and regulation.