English: Experimental BR Mk.I S No.S1000, built by BR (Eastleigh) 1962 in GRP, in BR maroon livery. It never had a Lot number nor a Diagram number. At Mendip Vale, East Somerset Railway, 15 April 2018. The coach consisted of the new GRP body placed on the underframe of Mk.I TSO No.S4378 the body of which was destroyed in the 1957 Lewisham crash but the underframe of which was salved. Although some records show the frame as being from No.S4377 also involved in the Lewisham crash, other records show this frame was crushed and cut up on sight! Although No.S4378 was an express coach, it was decided to design the GRP body as a suburban compartment type as being simpler to mould. It was originally numbered DS70200 in the Departmental range because it was on trial and used only to convey BR staff to Lancing Works. It was later renumbered S1000S and placed into public service on the Hayling Island branch and subsequently the Clapham Jct. - Kensignton Olympia unadvertised service for Post Office workers. Although the suffix normally indicated a coach of pre-Nationalisation design, some trial/non-standard coaches also used the suffix, confusingly! The coach proved entirely successful but it was decided GRP was too expensive to use in production coaches. It carried green livery in BR service so it is not clear why the coach is now in maroon livery and does not carry the suffix in its number.