I have researched railways when making models of the prototype many times before, however researching an aircraft to model for the diorama was the first time I had explored the world of model aviation.
As mentioned before I wanted to make sure I featured a model of an aircraft that would be seen at the real time and location, Gatwick Airport in the mid to late 1990s, so it was not just about getting the aircraft type and the livery correct, but also the individual aircraft itself if possible, in order to apply the correct water-slide decal transfers.
One of the first places I looked at, was the website http://www.britishairways.com which showed (correct at time of researching June 2015) that the aircraft 737-400 is based exclusively at Gatwick Airport, the location of the diorama.
The next location I searched, after Google, was https://www.planespotters.net/ which tells us that the 737-400 fleet at British Airways had (correct at time of researching June 2015) four aircraft, of which the oldest was G-DOCF, having first flown in November 1991 and appears to only ever had one operator all its life, British Airways, this makes it very certain that it flew into and out of Gatwick in Landor livery.
Coincidentally, the very day I finished the scale model of the aircraft 29th June 2015, it ended up being taken out of service! It now appears to have been stored outside of the UK, probably pending scrapping.