A number of train services between Clapham Junction and Milton Keynes are being cancelled this morning (Monday).
National Rail said this was due to a "shortage of train crew".
The disruption is expected until 10am.
National Rail said customers may need to travel on alternative routes and journey times might be extended.
Southern tickets are being accepted into:
- Southern services into London Victoria
- London Underground services between Victoria and Euston/Harrow and Wealdstone
- London Overground services between Clapham Junction/London Euston and Watford Junction
- London Northwestern Railway services between London Euston and Milton Keynes Central
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