Taking any action to prevent one's arrest. A person may use reasonable force to resist an illegal arrest (Christie v Leachinsky  AC 573 (HL). If he resists a legal arrest, however, he lays himself open to a charge of assaulting or obstructing a police officer in the course of his duty. The fact that the police officer was in plain clothes is no defence to such a charge. The House of Lords has ruled that it is the right and duty of every citizen to take reasonable steps to prevent a breach of the peace by detaining the offender (Criminal Law Act 1967 s 3). The offender therefore has no right to resist such an arrest on the grounds of self-defence; if he uses force to do so, he may be guilty of an assault.
From: resisting arrest in A Dictionary of Law »