|Length:||22 miles (35.4 km)|
|Met:||A4, M4, M3, M25, A3|
|Now part of:||A329(M)|
|Route outline (key)|
The M31 was originally envisaged as an M3 – M4 Link Motorway. In the 1966 Travers Morgan report for the Ministry of Transport, four possible routes were included for the M31, with the so-called "Blue Route" and "Blue Route Extension" (which extended the route to the M25) being named as the Preferred Route. Copies of the report are in the Surrey History Centre in Woking.
The only part of this road to be built was the northernmost section, which was constructed and opened as the A329(M).