Thanks for all the suggestions. Finest Kind are playing near us with Coope Boyes and Simpson, or even nearer on their own so I'll have to try and get to hear them. Forgot to mention the Silly Sisters at the top - surprised they haven't been mentioned in the thread.
Someone mentioned the Shellbacks, and of course any shanty singing has great harmony potential and the best thing of all is that it's participatory. My fave shanty group is the Maritime Crew from Auckland, NZ they regularly play in the maritime museum there if anyone happens to be down that way ;-) F