The police have telephoned me and said they want to speak to me, but they won’t say why. They want me to go to the police station, and say that if I won’t go they will arrest me. Can they do that?
It depends what they think you’ve been doing and why they think you can help them. If you are asked to go “for questioning” or “to help with inquiries” you are entitled to refuse. The police must then decide whether they have “reasonable grounds for suspecting you are guilty of an arrestable offence” – in practice all serious offences, plus some others. In practice your solicitor will usually be able to sort it out with the police and arrange for an appointment with them, if you are advised to do so. Legal advice in the police station is free.