W80394 was originally constructed in 1956 as a side corridor passenger coach (SK) W25156. It was one of one hundred and twenty vehicles constructed to Lot 155 Diagram 147 and numbered 25045 to 25164. These were all allocated to the Western Region. In 1967 it was one of fifteen vehicles converted at York under Lot 30900 Diagram 726A to a Post Office Sorting Van (POS) (TOPS design code NS531). They were given numbers 80381 to 80395 and allocated once again to the Western Region. Diagram 726 made no provision for nets or arms which were the devices used for exchanging mail bags while on the move. The order for the conversion was issued January 1975 and completed in August 1977. It was allocated to Old Oak Common depot and was transferred to Euston in 1993. It is fitted with B5 bogies and has electric train heat. W80394 originally carried corporate British Rail blue and grey livery and acquired its current Post Office red livery in 1989
It arrived at Quainton after storage at Willesden on 22nd February 2007.