I'm not sure quite how the question of "austerity" crept in here. Tax avoidance schemes were in existence long before this country's present financial difficulties.
I agree that no one should pay more tax than they are required to do but the rich can afford to employ financial advisers who seek out the gaps in any one country's tax laws and the differences between the arrangements in different tax jurisdictions and exploit those gaps. Those advisors can be quite creative but, sometimes, create what I would regard as artificial arrangements to avoid their clients paying tax. For example, to the best of my knowledge, neither MK nor his former wife has any genuine connection with Jersey, which has a tax regime that encourages such arrangements. While I am as cynical about politicians as the next person (possibly more so than most), most governments are playing "catch-up" all the time, while other governments set out to establish financial structures deliberately to attract the money of the rich.
The average person cannot afford to employ these financial advisers. What is irritating is that certain of the rich who do use these somewhat artificial schemes are the very people who express concern about the downtrodden working man and woman, seemingly oblivious to the fact that the less well off pay more tax because the rich pay less than their share.
Such tax-avoidance schemes may or may not be well-known and may or may not be above board but there is a moral dimension to everything in life.