The principle that abusive practices are prohibited must be interpreted as being capable, regardless of a national measure giving effect to it in the domestic legal order, of being applied directly in order to refuse to exempt from value added tax sales of immovable goods, such as the sales at issue in the main proceedings, carried out before the judgment of 21 February 2006, Halifax and Others, was delivered, and the principles of legal certainty and of the protection of legitimate expectations do not preclude this.