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|carno = 2559425686|livery = Green (unlined)|othernos = S25594M25686, W25686, W18686

}}The BR Mark 1 Corridor Second (SK) was the most prolific of the Mark 1 passenger stock, with more than 2,200 built. Those in the Western and Southern regions seated eight per compartment, while those on Midland and Eastern routes seated six per compartment. Early examples featured veneered walls, while later batches used formica laminates. The SKs were an early candidate for withdrawal, being replaced by Mark 2 Open, HST sets and Networker Turbo units.<ref name = StockBook>SVR Stock Book 9th edition</ref><ref name = SVRCT>SVR Charitable Trust</ref>.

BR Mark 1 Corridor Second (SK) ==Service and preservation==25686 was built at Wolverton in 1958 to diagram number Diagram 146 of lot number (AA201), Lot 30426.It entered service in the London Midland region in 1958, transferring to the Western region in June 1981. In September 1983 it was renumbered W18686<ref>Railway Heritage Register Carriage Survey[[Bibliography#Other References|Longworth (2013)]] pp.143-4, 119.</ref>

25686 arrived on the SVR in December 1986 from Old Oak Common. It is owned by [[Severn Valley Railway (Holdings) PLC | SVR(H)]] <ref name = StockBook/> and is one of four such coaches used converted for use as staff accommodation at [[Bridgnorth]], where it can be seen in "George's siding" adjacent to Platform 1.