There is no specific requirement for evidence of competence other than that stipulated by the vessel's flag state.
A valid ICC should be acceptable evidence of competence as Resolution 40 has been formally adopted by the United Kingdom.
The Bailiwick of Jersey and the Bailiwick of Guernsey are Crown Dependencies. There are two customs authorities:
Bailiwick of Guernsey (for Guernsey, Alderney, Herm and Sark) requires you to clear customs on arrival - fly your Q flag and complete and return the customs form which will be supplied to you at your port of entry.
States of Jersey do not require yachts to fly the Q flag and fill out the JCE 112 declaration from unless they have arrived from outside the EEA, have non EEA nationals onboard or have any goods to declare (including prohibited or restricted items).
The Channel Islands and UK are separate customs authorities. When returning to the UK from the Channel Islands, you must report your arrival to UK customs.
There is a reciprocal health agreement between the Bailiwick of Guernsey and the UK. Details of this agree are available on the States of Guernsey website.
Please refer to the States of Guernsey website for further advice.
There is a reciprocal health agreement between Jersey and the UK. Details of this agreement are available on the States of Jersey website.
Guernsey harbours: http://www.harbours.gg/
States of Guernsey: https://www.gov.gg/
Port of Jersey: http://www.ports.je/JerseyMarinas/Visitors/Pages/default.aspx
States of Jersey: https://www.gov.je/Pages/default.aspx