The class 207 is the last incarnation of the BR MkI design diesel electric multiple unit. Unlike most diesel multiple units (which have mechanical drives) the power cars on DEMUs are effectively mini diesel-electric locomotives with final drive by electric traction motors. This was the Southern's preferred form of multiple unit away from the third rail juice, governed by commonality with the EMU fleet of many components for maintenance purposes.

The entire class of 19 three car units were built in 1962 for the Oxted line. They were originally formed motor brake second saloon (MBSO), trailer composite lavatory (TCL) and driving trailer second semi-saloon (DTSO). The MBSO contains a 8ft 2in guard's and luggage compartment. They are similar to the earlier 3H units although there are a number of differences. The cab ends made of steel reinforced fibreglass are similar to contemporary EMUs such as 4 Cigs. The driver's desk is also to a revised design. Being built to run between Tonbridge and Tunbridge Wells West, a route notorious due to its Somerhill Tunnel with restricted clearance, the bodywork is built to 8ft 6in width. Although their engines are of the same type as other Southern Region DEMUs their mounting arrangements are different and thus they are not readily interchangeable.

There have been reformations over the life of the class. In recent years they have been reformed as standard class only 2 car sets (class 207/0) and 3 car (207/2) containing a former refurbished 4 Cep trailer second (TS) released by withdrawal of the Cep units and reformation to 3 Ceps. In this latter case the difference between body widths is obvious. With the diminution of work for DEMUs on the former Southern Region their sphere of operation has also increased to take in the Ashford to Hastings "Marshlink" line. In terms of surviving in quantity the 207s have fared slightly less well than the earlier 205 DEMUs with only 4 units (one 205/0 and three 205/2) - 21% of the original fleet - remaining by 2001.

photograph by Keith Harwood

photograph by Keith Harwood

photograph by Keith Harwood