[4] The railway line served the following Sussex communities: Polegate, Hailsham, Hellingly, Horam for Waldron, Heathfield, Mayfield, Rotherfield and Eridge.

The Cuckoo Line was built by the London Brighton and South Coast Railway (LB&SCR) in two sections, starting with the branch from Polegate to Hailsham which opened to traffic on 14 May 1849.

The route continued north-eastwards, leaving the Oxted Line at Birchden Junction heading for Groombridge, High Rocks Halt and eventually Tunbridge Wells West.

On 1 September 1897 at Tooth's Bank, 2 miles north of Heathfield, the 08:18am service from Eastbourne was running around 4 minutes late and was trying to pick up time in order to meet a connecting train at Groombridge.

Driver James McKinlay was killed and Fireman Lewis Minns seriously injured, whilst 30 passengers suffered minor injuries.

As the freight train service between Hailsham and Heathfield was due to be withdrawn the following month it was not considered worthwhile repairing the bridge so the line was prematurely abandoned forthwith.

The closure of this section was hotly disputed[6] – even British Railways itself agreeing that Hailsham was a growing town and that buses would be unable to cope with the demands of the increasing population.

Soon after closure of the Eridge to Tunbridge Wells West section, a preservation society was formed with the intention of reinstating the passenger service on the line.

The Tunbridge Wells and Eridge Railway Preservation Society (TWERPS) acquired the line in March 1996 and by December 1996 had started to run a steam-hauled passenger service along part of the route.

The line has been marketed as the Spa Valley Railway and it has gradually extended services with the most recent section to Eridge opening on 25 March 2011.