The Corridor First type of railway coach was one of the standard mid-20th century designs; coded 'FK' by the LNER and BR, and 'CL' by the LMS.

The layout of the coach was a number of compartments, all of which were first class, linked by a side corridor.

A number of the Mark 2A/2B/2C carriages were declassified in 1985 to become Standard Corridors (coded SK).

However, some electric multiple units based on British Rail coaches have first class compartments.

As of 22 May 2010 there are no more Mark 1-based class units in use (the last journey was on the train which left Lymington Pier on Saturday 22 May 2010 at 22:14 BST).