‘Avoidance’ is – whatever your views of its moral quality – lawful. ‘Evasion’ usually involves deception and is unlawful. You go, theoretically at least, to prison for offshore tax evasion. (‘Theoretically’ because HMRC tend not to bring prosecutions for this type of behaviour. As of November 2015 there had been only 11 prosecutions for offshore tax evasion in the last five years.)
In the coming days professional firms and others whose business it is to service or speak for those amongst the wealthy who prefer not to pay their taxes will be out in force in the newspapers and the media channels. Having assets in, or which have passed through, Panama is consistent with avoidance, they will tell you.
They – and, too, the Government which will want to defend its record in this field – will suggest that the outrage you feel about what you read you are wrong to feel. And that people can perfectly lawfully have assets in Panama. And that you cannot conclude from the fact that name X or name Y has appeared in the Panama Papers that X or Y has done anything wrong.