The express train service to Gatwick airport from central London was suspended on Friday after a signal failure caused major disruption on busy routes across the South East.
Network Rail said a fault with the National Grid power supply meant power was lost to all signalling over a wide area, including Southern’s Brighton Main Line north of Redhill, the Uckfield line and the East Grinstead line.
All trains were stopped while the power was off for a period before 7am and passengers were warned it would take until at least 4pm for services to return to normal.
Trains across the whole Gatwick Express, Southern and Thameslink networks may be cancelled or delayed by up to an hour, it was announced.
Gatwick Express services from London Victoria were suspended.
There were also technical difficulties affecting information screens at stations possibly showing incorrect information.
Station staff were instructed to make additional announcements.