Okay, further to my previous post, here's what I have so far in my search for fictional British islands. Thanks to those who've suggested some... anyone know of more?
ArmorelA fictional Channel Island based on Sark, from Jerrard Tickell's novel Appointment with Venus.
Qwghlm
From Neal Stephenson's Baroque Cycle. As I haven't read any of these books I don't know where it's meant to be located and can't find this info online, but I can tell you it's pronounced
Tagum.
Scylla
One of the Scilly Isles, from the 1989 British film
When the Whales Came, based on Michael Morpurgo's book Why the Whales Came (which does not feature a fictional Scilly Isle).
SodorFrom the Railway Series of books by Rev. W. Awdry, situated between the Isle of Man and Cumbria. Looking at the Wiki article, I'm also interested to see Sodor has a conlanguage, 'Sudric' - I wonder how far (or how little) it was actually developed. (Conlanguages are
another interest of mine).
St. Gregory
From the TV series
Island at War, a fictional amalgam (and replacement) of both Jersey and Guernsey.