I'm not sure. We need "an English-speaking island with a population of more than 20 million." British people sometimes consider being an island a part of their national identity, and that would be my first guess. The growth projection seems to fit since the population of Great Britain is about 60 million. In a famous speech in Shakespeare's play "Richard II," a character speaks lovingly of "This royal throne of kings, this sceptred isle, This earth of majesty, this seat of Mars, This other Eden, demi-paradise, This fortress built by Nature for herself Against infection and the hand of war, This happy breed of men, this little world, This precious stone set in the silver sea, Which serves it in the office of a wall Or as a moat defensive to a house, Against the envy of less happier lands, This blessed plot, this earth, this realm, this England." I'd wondered for a second about Ireland, but it doesn't fit because its population is only about 4 million (for Ireland itself) (plus 2 million for Northern Island). There is a small island, one of the Shetlands, that is actually named "Fair Isle," best known to me for a style of knitted sweater called a "Fair Isle sweater," but that obviously is not what's being referred to here. Its population is 55.

I don't know the context or origin of this quote, but it seems to suggest that the piece was written from and about an island nation, as the writer says that everyone in this beautiful island will be on Twitter soon.