There are various sources for information on the latest restrictions in force due to the Coronavirus pandemic:
RYA Covid-19 hub - https://www.rya.org.uk/coronavirus including advice and information for recreational boaters at https://www.rya.org.uk/coronavirus/advice-for-boaters.
Information on entry requirements can be found at https://www.gov.uk/uk-border-control?priority-taxon=774cee22-d896-44c1-a611-e3109cce8eae
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.
Visitors to the Bailiwick of Guernsey in the Channel Islands should note that the UK Department of Heath does not currently have a reciprocal health agreement with the Bailiwick of Guernsey.
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