Hi, Morwen -
I'm surprised that Gordon didn't come up with the attribution to Lord Invader / Rupert Grant. It's listed under Grant's name at the Harry Fox Agency songfile.com service - but there are several songs titled "Small Island," with different songwriters.

It is devilishly hard to verify the authorship of Calypso songs - so even though it may be claimed by Lord Invader, what proof have we? Most of the well-known calypso songs were claimed by either Lord Invader or Lord Burgess (Irving Burgie), but is that true? Besides, Bok's version is quite different from the version you attribute to Grant. It would be interesting to hear Harry Belafonte's view of this.

-Joe-