thanks for your advice - and for moving the thread to the right forum (sorry - blame a newbie)
My travel agent apparently isn't 'allowed' to sell me individual sector upgrades, only the whole return which I don't want (as it is way too expensive!). The travel agent refers me to MAS...who then refer me back again.
MAS have seen my post here, and have asked for me to DM them directly.
I'll let you know how I get on.
And thanks again for your help - excellent forum