Rail services on some of the country's busiest routes were disrupted on Sunday because of a series of incidents.
South Western Railway warned passengers that train services running across the whole of its network may be cancelled, delayed or revised until the end of the day.
A damaged cable between Putney and Clapham Junction in South London blocked one of the lines, a speed restriction over a defective track at Wimbledon meant trains had to run at 5mph on one of the lines heading away from London, a points failure near Basingstoke delayed trains, a signal failure at Frimley in Surrey meant trains had to stop and seek verbal permission to pass through when heading towards Guildford, and a freight train awaiting a member of crew at Raynes Park temporarily blocked one of the lines towards London.
The incidents, together with planned engineering outside Waterloo station in London, have had a "significant" impact on services, the company said.
A message to passengers said: "Trains are delayed across the network, and some may be altered or cancelled in order to reduce congestion."