From UK Immigration on the Gov.uk website
Your passport or identity card will be checked when you arrive at a UK port or airport
to make sure you’re allowed to come into the country. It must be valid for the whole of your stay.
You may also need a visa to come into or travel through the UK, depending on your nationality.
There has been no change to the rights and status of EU nationals in the UK, and UK nationals in the EU, as a result of the referendum.
What you can bring with you depends on where you’re travelling from. You must declare to customs:
- anything over your duty-free allowance
- banned or restricted goods in the UK, eg meat and dairy products from most non-EU countries
- goods that you plan to sell
- more than €10,000 (or its equivalent) in cash, if you’re coming from outside the EU
- You and your baggage may be checked for anything you must declare.
I read that as it is your obligation as the skipper
of a private vessel to ensure you and your crew clear in through Immigration and Customs on arrival in UK regardless of where you departed from, where you are resident or what passport you are travelling on.
As EU Citizens the process would be straightforward and simple but still needs to be undertaken or you may be considered Illegal Immigrants.
Even Sir Robin Knox Johnson cleared back in at Falmouth after his successful solo round the world
sail. When asked by Falmouth Immigration "where from?" he replied "Falmouth" having cleared out from there months previously but never having landed anywhere else in the trip.