Commuters have endured a difficult return to work due to problems on main line trains as well as the Tube.
Passengers on the busy London to Scotland East Coast line suffered morning rush-hour delays in a knock-on effect from last night's severe disruption between Peterborough and London.
This was due to overhead wire problems at Huntingdon in Cambridgeshire and affected not only East Coast passengers but those travelling with First Capital Connect, First Hull Trains and Grand Central.
Repairs have now been completed but passengers were warned to expect disruption until 10am.
There were also hold-ups for passengers in East Anglia due to over-running engineering works at Ipswich. Services between Ipswich and Felixstowe were suspended for a time and a limited bus service ran between between Stowmarket and Ipswich.
On the London Underground, there were severe rush-hour delays on the Northern line due to earlier engineering work.
Mick Cash, acting general secretary of transport union the RMT, said: "We have been warning for years that cuts to staffing and maintenance on the overhead lines have left them as a weak link in our rail infrastructure. Those warnings have been ignored and last night and this morning passengers have been left to pay the price.
"The solution is to clear the maintenance and renewals backlog and employ more staff or we will see this morning's transport chaos on rail and Tube repeated throughout the winter."
A spokesman for the East Coast train company said Network Rail (NR) engineers worked through the night to repair the damage at Huntingdon.
He said: "As anticipated, there has been some further disruption at the start of today's East Coast services. However, while trains are now gradually returning to normal, some services may continue to be restricted, and subject to short-term amendment or cancellation.
"Advance booked tickets dated for travel on Monday or Tuesday will be valid for travel on Wednesday, and customers are advised to try to travel as close as possible to their original booked time.
"East Coast is very sorry for the disruption this may have caused to your travel plans, and continues to work closely with its infrastructure provider NR to restore a good service again."