Dottymo - not Glenn but I'm 99% certain shellac is not yacht varnish. I think that's what we would call spar varnish - it's tough stuff, very waterproof and non-reversible. The only other name I've seen shellac commonly referred by is French Polish, though that's properly an application method. Here's a link to one company on your side of the pond that lists it:
http://www.mylands.co.uk/products/polishes/