It looks like we don 't need to worry too much yet. I got this reply from the RYA when asked.

Dear Mr Kynaston

Thank you for your enquiry.


At present there are no exit checks for recreational craft. There is no mechanism for putting such checks in place and the are no plans to put such checks in place this summer.

Details of the reporting arrangements for arrivals and departures from the UK vary depending on whether your first / last port of call is EU or Non EU. It is explained in detail at http://www.rya.org.uk/infoadvice/boatingabroad/Pages/customsformalities.aspx and for members further information is at http://www.rya.org.uk/infoadvice/boatingabroad/Pages/FormC1331.aspx


Kind regards

Carol

Carol Paddison
Cruising Advisor
Royal Yachting Association

The UK has started checking the credentials of anyone leaving the UK. There are no specifics for pleasure craft yet. Please post information you find here. Thank you!

Story here: https://uk.news.yahoo.com/passports-checked-uk-exit-025043682.html#z5TmsEe

Fact sheet here. https://www.gov.uk/government/publications/exit-checks-on-passengers-leaving-the-uk/exit-checks-fact-sheet

Vice Commodore, OCC