There is no such thing as aA written "street caution" in UK does not go on your criminal record. That's just a copper ticking you off with a warning that may be considered if you offend again.
An official caution that becomes part of your police record involves a visit to a police station, where you go through a process.
If you haven't had an official caution, then you've done nothing that needs to be declared, but you should get legal advice.