I found this old road atlas that covered the UK and showed the road network in Kent in 1964 when the M2 motorway had just been built and opened and the M20 was known as the A20(M) and only bypassed Maidstone from Allington to Hollingbourne. It's hard to imagine now but the M20 was only completed in 1989 to link Hollingbourne to Folkestone!
Road Atlas of Great Britain 1964 - Front cover
Plan of UK Motorways 1964
Start of M2 going off page
Map showing the new M2 opened in Kent 1964
Map showing the A20(M) Maidstone Bypass now known as the M20