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}}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) ==25771 in service==25771 was built at Derby in 1961 to diagram number 146 of lot number 30685.<ref>Railway Heritage Register Carriage Survey</ref> 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>

==25771 in preservation==25771 arrived on the SVR in September 1986 from London’s Old Oak Common, courtesy of the [[The 75069 Fund]]. It was formerly part of the [[Carriages#Set_M|BR Maroon ]] running set but has .  It spent some time in [[Carriage Repair Works|Kidderminster Carriage Works]], having been photographed there in 2007 for the Railway Heritage Register Carriage Survey and in May 2015 on Facebook.

In 2015 25771 was thoroughly overhauled at [[Carriage Repair Works|Kidderminster Carriage works Works]], having been photographed there in in May 2015 on Facebook, and outshopped in a later variant of BR maroon livery-with maroon ends. Appropriately the interior is typical of latter day Mk 1, being clad with light grey patterned Formica. For the present its primary function is to replace vehicles from Set N that are withdrawn in turn for overhaul, but once that programme is completed this very useful carriage is certain quickly to quickly find other work.