Ice has been blamed for train delays affecting, among others, Brighton and Hove Albion fans heading to Old Trafford for the Manchester United match today (Saturday 25 November).
Network Rail said: “Ice is preventing trains getting electricity from the third rail which has resulted in trains having to run at reduced speed on some lines.
“Train services running across the whole Southern, Thameslink and Gatwick Express network are returning to normal but may be cancelled or delayed by up to 20 minutes.”
Disruption is expected until 1pm, Network Rail said: “During low temperatures, the electrical third rails become icy preventing our trains from receiving power.
“This results in services having to proceed at a reduced speed, and at times come to a halt.”
The stretch of track between Haywards Health and Balcombe was the worst affected on the mainline this morning.
Elsewhere on the network there were problems between Brighton and Eastbourne as well as further east between Hastings and Ashford International.
Network Rail added: “Earlier this morning services between Lewes and Ashford International were suspended due to severe icy rails.”
Southern laid on replacement buses for a few parts of the network where several services had been cancelled.
Customers were being told: “Please be advised that where train service has resumed, delays and alterations to services are still likely.
“Southern advise that you allow extra time and check the journey planner prior to travelling.
“You are also advised to take extra care when boarding and alighting services today as platforms are likely to be slippery.
“If you are a Gatwick Express customer, your tickets will be valid for travel between Brighton, Gatwick and London Victoria / London Bridge via Southern and Thameslink.
“If you are a Southern or Thameslink customer, your tickets will be mutually accepted across the Network this morning on Southern and Thameslink services only.”
Some Albion (and Man Utd) fans also suffered delays in traffic jams on the M6.