The Magistrates' Court had erred in holding that a police officer had had reasonable grounds for suspecting that the appellant had committed the arrestable offence of possession of an offensive weapon in a public place and therefore that the police had arrested him in the lawful execution of their duty.Appeal by way of case stated against the decision of Carlisle Magistrates' Court on 14 October 2002 to convict the appellant ('M') of resisting a police constable acting in the execution of his duty contrary to s.89(2) Police Act 1996. The police had received a report that a man had threatened the occupants of a house with a hammer ('the earlier threat') and were later called to the vicinity of the address given because a man matching a description given to them had been spotted. The police found M with a hammer which he gave up to them. The police then sought to arrest M for possession of an offensive weapon in a public place, which arrest M resisted. The offensive weapon charge was later withdrawn. In respect of the charge of resisting arrest, on a submission of no case to answer and on the present appeal, M argued that: (i) because a hammer was not an offensive weapon per se and the case against him was based on the earlier threat and not carrying the hammer in a public place with offensive intent, the prosecution had to show that the police had not only had reasonable grounds for suspecting that an arrestable offence had been committed but that they had in fact done so; (ii) the police had not had such reasonable grounds for suspicion because there had been no consideration of whether the alleged offence had happened in a private or public place; (iii) there was therefore no evidence of one of the key elements of the offence; and (iv) accordingly, the police had not been acting in the execution of their duty when they had arrested him.HELD: (1) The Magistrates' Court had erred. There was no evidence that the police had reasonable cause to suspect that M had been carrying an offensive weapon with intent to use it for offensive purposes at the time of his arrest. (2) The Magistrates' Court had focused only on whether there were reasonable grounds for suspecting that an arrestable offence had been committed in relation to the earlier threat and there was no evidence as to whether that offence had been carried out in private or public. (3) The court below had not considered the possibility that the police may have suspected that because of the earlier threat they might have had reasonable grounds to suspect a future threat. If it had done so it might have found such grounds but the Divisional Court could not go behind the findings of the court below. (4) Accordingly, the police had not been acting in the execution of their duty when they had sought to arrest M (Chapman v Director of Public Prosecutions (1988) (1989) 89 Cr App R 190 followed).Appeal allowed.