I've been to Sea, not as far as the NL, admittedly, it's a can of worms innit, you know you could probably get away with it, but sod's law says you will get caught, then hung ,drawn & quartered !
Speaking of which, having been at sea, it used to be the case, if you are British, you could sail into your home port, and generally not get molested by the 'feds' as long as you are flying the red duster, it don't work the other way , enter any continental port whilst flying the Red Duster, ( which you have to, it's kind of a passport) you will get a visit from the foreign 'feds', so it isn't on to have a nice shiny new bike on board ,with no paper trail for it .
For now, the risk isn't worth it, I know I could get away with it, , I I've never been stopped , cycling through passport control apart from the usual checks, and get waved through the Green channel,