[3] The Mole Gap between Dorking and Leatherhead is one of the few natural breaches in the North Downs and its potential as a rail corridor was realised as early as 1830 when a line linking London to Brighton was proposed.

The scheme failed to attract sufficient investment and was dropped in favour of the Woking, Guildford and Havant route from London Waterloo.

Initially services ran from London Bridge to Brighton via Sutton and Steyning, four times per day in each direction.

The Southern Railway, formed in 1923, began an extensive programme of electrification of their suburban lines.

The line from Waterloo to Dorking was electrified using the 660 V third rail system in 1925 and regular half-hourly semi-fast services were introduced on 12 July 1925 to run seven days per week.

The 22+1⁄2 mi (36 km) journey to Waterloo originally took 45 minutes, although this was considerably lengthened when trains began to stop at all stations shortly afterwards.

Additional hourly electric services to London Bridge via Mitcham Junction and Tulse Hill began on 3 March 1929; the 25 mi (40 km) journey took 53 minutes.

These gave commuters from Dorking their fastest ever link to London Victoria – 34 minutes during peak hours.

The off-peak service provision of two trains from London Bridge to Horsham via Sutton and Dorking existed for a number of years from about 1985 but ceased by 2000.