The 1st-rate stamp in the series features the rood screen and choir at Lichfield Cathedral, northwest of London. Established some 1300 years ago, the cathedral began as a shrine to house the bones of Chad, and later was the site of a Norman church and then a Gothic Cathedral, with substantial alterations in the 18th and 19th centuries. The choir program of the cathedral maintains its own website, with information about the organ. The present organ dates from 1884, with the most recent work being done in 2000 by Harrison and Harrison. A nicely detailed specification may be found here. The casework for the choir-facing section of the organ is barely discernible in the stamp image.
Update 4/2011: The current issue of the Jounral of The Organ Club (of Great Britain) has an article that includes information on the Lichfield Cathedral organ. The Club visited the cathedral and other local sites on the 21st of August 2010. The article includes notes on the cathedral itself and information about the organ, including reflections on Club members' playing of the instrument, and a current stop list.