There is major disruption on the Thameslink line this morning after a signalling problem in London.
Trains are not running through Streatham Common after Network Rail experienced of a total loss of signalling power on three separate lines in that area.
St Albans passengers travelling to Streatham should expect delays of up to an hour, alterations and cancellations.
The problem also affects trains between Luton and Wimbledon, which are currently suspended.
This is anticipated to continue throughout the whole day.
People are also advised not to travel via London Victoria as there is a very limited service from Southern, Thameslink and Gatwick Express.
Tickets are being accepted on other lines via any reasonable route.
Replacement buses are in the running for between East Grinstead and Three Bridges, Oxted and Redhill, Oxted and Caterham, and Uckfield and Tonbridge.
There was also disruption at St Pancras last night in a separate incident which the emergency services attended.
That was cleared at about 2am this morning.
For more information, visit www.nationalrail.co.uk/service_disruptions/195079.aspx
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