Rail commuters are facing mayor disruption after engineering works overran.
South Western Railway services between Surbiton and London Waterloo, the UK’s busiest station, only began running at about 10:00 GMT.
Disruption on SWR services is “expected until the end of the day”, after Network Rail work, due to finish at 04:30, was delayed.
Normally packed rush hour trains were cancelled, leaving thousands stranded.
One passenger blasted the travel chaos as “a complete and utter shambles”, with another suggesting “critical jobs” such as teachers, doctors and nurses would be affected.
Southern services between East Croydon and London Victoria have also been hit by over-running engineering works.
Network Rail has apologised to passengers, while SWR has warned that services across its entire network may be cancelled, delayed or revised all day.
A Department for Transport spokesman said: “We share the frustrations of passengers trying to get into London this morning.
“The disruption is unacceptable, and we are seeking an urgent explanation from Network Rail as to why their engineering works have overrun.”
Rail passengers have taken to social media to complain about the disruption.
Network Rail’s overnight work in the Hampton Court area was originally due to finish at 04:30 GMT but overran, with a completion time of about 08:40 then mooted.
In a statement shortly after 10:00 SWR said: “All lines have now re-opened. Network Rail has now completed their work.”
All lines and closed stations including Woking, Surbiton, Raynes Park and Earlsfield have now reopened.
However, Silvia Mendes described it as “complete and utter shambles” while Richard Sansom simply posted: “You have got to be kidding me @SW_Railway.”
A long-running dispute over the role of guards on trains has previously crippled SWR services because of strikes.
SWR operates from London Waterloo to Berkshire, Surrey, Hampshire, Dorset, Devon, Somerset and Wiltshire.
A message to passengers at about 05:00 advised people not to travel on SWR services due to the disruption.
A Network Rail spokesman said: “We would like to apologise for the disruption to passengers’ journeys on South Western this morning.
“This is due to over-running engineering works in the Hampton Court area.”
Passengers have also been told that trains across the whole Southern and Thameslink network may be delayed, cancelled or revised on Monday morning due to over-running engineering work at various locations, with disruption continuing until noon.
The rail operator said services may be cancelled or diverted via London Bridge.
The Rail, Maritime and Transport (RMT) union called for the resignation of Transport Secretary Chris Grayling after what it called the latest railway “meltdown”.
General Secretary Mick Cash said: “While the crisis on our railways deepens, the Transport Secretary Chris Grayling is markedly absent… He should go, and he should go now.”
Lib Dem MP Ed Davey, who represents Kingston and Surbiton, tweeted: “Commuters will be extremely angry today that, after 18 months of appalling services, stations are shut and trains cancelled due to Network Rail failing to do engineering works on time. When will Grayling act?!”
Tooting’s Labour MP said the response to the disruption was “not good enough”.