You're nicked

Under provisions set out in section 25 of the Police and Criminal Evidence Act, the police can arrest you for a non-arrestable offence only if general arrest conditions apply. One such condition is a reasonable belief that you have given a false name. Nevertheless, even under these circumstances, before the police can arrest you they must also ask for, and presumably check, your address. In Mr V's case, the officers failed to do so.
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At the trial, I argued that the police hadn't had reasonable grounds for making an arrest as they hadn't asked Mr V for his address once the reasonable suspicion about his name arose. If general arrest conditions didn't apply, then the officers had no power to arrest him and their actions were unlawful. Mr V was therefore entitled to resist. The magistrates reluctantly agreed and the charges were dismissed. For Mr V it was a moment of triumph: he'd been wronged and the court made it right. The officers were dumbstruck.

The distinction between arrestable and non-arrestable offences is important—it is a statutory limit on police powers. Or at least it used to be. On 1st January, the Serious Organised Crime and Police Act came into force. Buried away in part 3 of the act, section 110 removes the distinction. The effect is that the police can arrest you for any offence, even speeding. The reason for the change in the law was that the police, amazingly, found the distinction between arrestable and non-arrestable offences confusing and therefore inconvenient. If I were representing Mr V today, he wouldn't have the legal protection he was afforded 12 months earlier.

Alex McBride's Common law column in Prospect, April 2006.