P wanted to sue D for breach of a contract that distorted competition. English law does not allow a party to an illegal agreement to claim damages from the other party, but ECJ says that Article 81 of the Treaty requires that damages be available. ECJ held that an absolute ban on a claim for breach of an anti-competitive contract would contradict the ‘effectiveness’ of EU law. However, in the absence of community rules it is for the domestic legal system of each Member State to designate the courts and tribunals having jurisdiction and to lay down the detailed procedural rules governing actions for safeguarding rights which individuals derive directly from Community law, provided that such rules are not less favourable than those governing similar domestic actions (principle of equivalence) and that they do not render practically impossible or excessively difficult the exercise of rights conferred by Community law (principle of effectiveness). As such, NCs may implement EC laws so as to prevent them being used to unjustly enrich someone, so that EC law does not preclude a rule that only allows a claim for breach of anti-competitive contract where P was in such a weak position that his freedom to contract was impaired.