It is not just tax. Here in the UK there is also NIC involved. I can detect a cry for help in the message, sort of a PAN. I would suggest you consult an accountant who has had experience in precisely such a matter and within the aviation industry, and do not allow the matter to develop into a MAYDAY. The sort of an accountant you need is one who has had a great deal of grass roots level aviation experience. One who preferably is or was once a pilot. The number of days for any kind of tax dodging are dwindling fast. Not just here in the UK alone, but everywhere where there is some kind of law and order.