I know its been answered on here somewhere before, but when I see EGGW I can't help think the obvious answer is Gatwick when in fact its Luton. Anyone care to explain how that came about?
Yep!
There was a time when some major airfields acted as comms centres for others to connect to, they were the ones with the double letters at the end - EGLL, EGSS etc. Luton was EGLN and connected to the AFTN via Heathrow EGLL. When a 'new' comms centre was opened at Croydon that became EGGG and Luton's link was transferred to it and became EGGW. I guess W was just a spare letter although I think this explanation falls down a bit when you consider that Shawick Oceanic is EGGX! At around the same time Elstree's AFTN link was moved from Heathrow to West Drayton so changed from EGLE to EGTR.
Today it doesn't work like that but, by and large, they do seem to be allocated geographically.