International Certificate of Competence
Any British Citizen or British Resident sailing outside of the UK should have an International Certificate of Competence (ICC)
The ICC is issued by the RYA after a practical and oral examination covering basic navigation, seamanship, and handling. It is very useful for skippers cruising in foreign waters, particularly if you are skippering a foreign-flagged vessel. Port Police expect to see your ICC and it is probably not worth arguing over the ins and outs of possessing it.