British Airways keeps a collection of documents, staff uniforms, aircraft models and aviation posters alongside a huge collection of photographs relevant to BA and the companies which now constitute them. The photographs of biplanes of the Imperial Airways Company are fascinating as are too the reproduction posters created to lure holiday makers to sunny climates.
http://discovery.nationalarchives.gov.uk/details/a/A13529964 Heathrow Airport Terminal 5 ( bit of a walk to Waterside )