The M26 came into being following the decision to turn M25 to the North to complete the ring via the Dartford crossing. Sometimes referred to as the Wrotham Spur it serves as a link between M25 and M20 and the Channel ports.

A decision was made not to provide an all-movements interchange at Sevenoaks, there being no provision for westbound to southbound turns. The decision was based on traffic needs and assumed that vehicles wishing to travel to destinations well to the south of Sevenoaks would have left the motorway much further back and used local roads. The additional link would have required land to be acquired from the Chevening Estate and the it is suggested that it was political considerations and not the traffic requirements that influenced the Department of Transport’s decision. Following renewed lobbying a further study was carried out in the late 1980’s but this confirmed the original decision that provision for the extra movement could not be justified.

Construction of the motorway took place between 1977 and 1980 without major problems apart from those associated with building on Gault clay, and being faced with the complete destruction by fire of the project office, along with the drawings and documents held there.