A friend of mine was transferred from London to the Paris office of his firm, together with several colleagues. They were happily spending their salaries, and then tax returns day came along. They assumed that PAYE worked the same in France, that they would have had the right amount of tax withheld by the company, and got quite a shock when they realised there was a huge shortfall and they should have been setting aside some of that money each month for their yearly tax settlement, rather than spending it on fancy restaurants. Oops!