More info from National Rail

Some details of the emergency service operating through Worcester Park because of the landslip have been posted here but to make your life a little bit easier I've reproduced them below:
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Train services between Epsom and Raynes Park are being disrupted due to emergency engineering works at Worcester Park.

To help deal with the greatest of passengers using services on this route, the levels of disruption at different times of the day will be as follows:

Morning peak (until 09:30)
The normal service between London Waterloo, Epsom and Dorking / Guildford is suspended and the following special service will operate:
- a half hourly service will run between London Waterloo and Epsom, calling at all usual stations; - a normal service between will run London and Chessington South, with a number of additional services operating in the London bound direction only;
- services between London and Guildford via Leatherhead will be diverted and not call at stations between Motspur Park and Bookham. Services from London will call additionally at Surbiton and Effingham Junction and services to London will call at all stations between Guildford and Surbiton via Oxshott and also at Raynes Park.

Daytime and evening (between 09:30 and 15:30 and from 19:00 until end of service)
As morning peak, although the additional services from Chessington South to London Waterloo will not run.

Evening peak (between 15:30 and 19:00)
As morning peak, although additional services will run from London to Chessington South only.

In addition to the above, replacement bus services will run between Malden Manor and Leatherhead and between Leatherhead and Effingham Junction, calling at all stations.

South West Trains passengers may travel on Southern services. Customers wishing to travel between Dorking and Epsom should use Southern services.

London Underground are accepting South West Trains passengers between London Victoria and London Waterloo.

This disruption is expected to continue until Monday 17 December.