A failure of the electricity supply in Southern England is causing disruption to all services across the Gatwick Express, Great Northern, Thameslink and Southern network.
Services may be cancelled, delayed or revised until the end of the day.
This problem is also affecting East Midlands Trains services to and from London St Pancras Internationaland LNER services to and from London Kings Cross.
The UK Power Network has failed in the large parts of London and the South East. This has prevented trains across the Great Northern network and between Farrigdon and Bedford from being able to take power and as a result, most trains are currently at a stand.