Those wanting to engage in Coastal Canoeing should consider adding their craft to Small Ships Register (Part III): this "provides an inexpensive, simple registration which proves the ships nationality (a kind of passport)".
In UK waters, the CG66 scheme should be sufficient (though the SSR wouldn't hurt)... but CG66 allows you to enter your craft's Small Ships Registration Number: the two systems are complimentary. Advantages to the SSR might emerge if coastal canoeing elsewhere: I'm not aware of any British Canoe Union guidance, but the Royal Yachting Association offers [url="http://www.rya.org.uk/infoadvice/boatingabroad/Pages/boatingabroadpaperwork.aspx"]a very helpful page[/url].
The guidance notes say the new SSR application costs £25, with the registration being valid for 5 years: three months before your registration is due to expire, RSS will apparently send a renewal notice to the address you registered with them... but that must currently be accompanied by a further £25 fee.