If there are legitimate ways of avoiding tax and vat then utilise that. I think many Scholars would disagree also on the point that you should abide by the rules of your country. On the other hand some people have cash in hand jobs and their employer wouldn't want to show them working full-time as this would incur employer tax and national insurance contributions on the employer, so in many instances the employer to save money wouldn't want to show the employee working full-time to hmrc (uk) - and the employee i feel wouldn't be at fault because he needs to earn a living. Wallahu A'lam.