Reasonable suspicion that you are breaking the law, or are about to break the law. They may be required to justify their grounds, i.e. what they suspect you of

Reasonable suspicion that you are breaking the law, or are about to break the law. They may be required to justify their grounds, i.e. what they suspect you of and why. They have been known to simply ignore those requests for why. e.g. I suspect you of going equipped to commit burglary due to your stripey jumper, crowbar and bag with "swag" printed on it. Proving ID is usually done via passport or driving licence. If you don't have those producing a couple from bank statement, utility bill or council tax bill is usually enough. I'm old enough to have got bank account without any requirement for ID at all. Yes, that means it can be a chain of circumstantial evidence rather than proof.