Ah well, back to the old days ... or not
When I first started sailing, the procedure for leaving and entering the UK on your own boat was fairly simple. You had to fill in form C1331 and pop it in the special post box on the wall of your local port customs post before you left. When you returned, you had to call port customs on VHF. You could moor your vessel, but otherwise no-one could leave the boat for an hour after tying-up. If no customs officers arrived, after an hour you were free to disembark. We used to obey this quite religiously; moored on some lonely east-coast creek with the lights of the pub in sight, we would obediently huddle in the cockpit for the prescribed hour, with not another human being in sight. That's being English, I suppose.
Our semi-Shengen arrangements in recent years have meant that if sailing to and from other EU nations, you don't need to notify anyone in the UK at all. Just come and go. The French of course still preserve the old civilities, and when the French border police board you (as they will) on arrival (a) it is perfectly normal to offer the officers a small glass of red wine each (b) you will be expected to produce Certificate of Registration, passports, International Certificate of Competence, Insurance documents, radio apparatus licence, radio operator's licence and of course the vessel's log-book, properly completed in ink and not pencil. Friends have found a small rubber stamp and ink-pad inscribed with the boats name and registration number also engenders a small frisson of excitement amongst these gents; they will solemnly produce one of their own, and a small satisfied flurry of mutual stamping will occur (c) at this stage, it is again normal to offer the officers a refill of red wine, which they will graciously refuse.
I have found these arrangements not to be onerous. Generally relaxed and good-humoured, it does give the impression that the French are serious and professional about these things. Yet if travelling by ferry, until recently it was unusual to find even a single French border official on duty at the major ports. Strange.
I suppose it's inevitable that Brown's announcement that every person entering and leaving the UK will be security checked will extend to the half a million pleasure craft in private ownership in the UK, although without re-opening customs posts in scores of minor ports it's difficult to see how this will be done. Oh yes, I forgot. This is Brown's Totalitarian Britain. He will simply forbid us from leaving UK territorial waters at all.