Rail passengers travelling to and from Sutton should expect delays until noon today.
Trains travelling from Sutton to central London are expected to have delays of up to 40 minutes.
The issue will also delay trains coming in to Sutton.
It is due to a major signal failure this morning at 6.19am between Blackfriars and Farringdon.
The problem has been fixed but delays are expected to continue until noon.
The disruption is a Network Rail issue and an auto ticket acceptance has been put in place so passengers can use alternative transport options.
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