If plod (either a constable, or in London, also a PCSO) asks you to stop, you must do so, without any reason.
If they (a constable only - PCSOs do not have the general powers of a constable, just designated powers) ask you to dismount, they must have a lawful reason - they do not necessarily have to tell you this reason, and it may be as vague as "directing traffic".
If plod (either a constable, or in London, also a PCSO) asks you to stop, you must do so, without any reason.
If they (a constable only - PCSOs do not have the general powers of a constable, just designated powers) ask you to dismount, they must have a lawful reason - they do not necessarily have to tell you this reason, and it may be as vague as "directing traffic".