My primary source of research was the internet. There is such a wealth of information online and both reference images and historical records were in no short supply.
Aircraft
A large part of my project is the aircraft that feature in the scene and being somewhat of an aviation enthusiast; I really wanted to get the aircraft as realistic and accurate as possible and so I relied heavily on Google and it's image search facility.
I also discovered two particularly helpful websites which helped me with the aircraft part of my project. The first website, epibreren.com*, provides visitors with extensive information about World War II Allied air operations; from squadron information such as aircraft, bases and missions to recorded aircraft and airmen losses during May and June of 1940. This website was particularly useful to me when designing the aircraft identification decals for my Spitfire models.
The second of the two helpful websites was fritzthefox.com**. Quite interestingly, Fritz the fox is a cartoon character who features in numerous comics strips depicting historical scenes from the world's various air forces. However the website has a really useful section detailing many facts about the comics' featured aircraft including various paint scheme details as well as aircraft identifier information and camouflage variations and their particular usage.
Below you can view the main images from fritzthefox.com that I used to accurately texture my aircraft models.
*http://www.epibreren.com/ww2/raf/index.html
**http://www.fritzthefox.com/british_camo_guide.html - thanks to Barry Munden
