Some rail passengers are still facing disruption at London's King's Cross station after weekend problems caused by overrunning engineering works.
The problems were caused by a signalling issue near Finsbury Park and congestion caused by the overrunning work, National Rail Enquiries said.
A revised service is now operating on Monday on Great Northern routes to and from King's Cross station.
Some trains into King's Cross were delayed by more than an hour on Sunday.
The station was closed throughout Saturday, causing major disruption.
Some trains, including services from Edinburgh, arrived about 90 minutes late into the station on Sunday. Some passengers arriving on late trains were provided with taxis home.
The Office of Rail Regulation is to investigate the disruption, which also affected services between London Paddington and Reading on Saturday, leaving Paddington temporarily closed.
BBC's Nick Eardley, at London's King's Cross
Things were looking fine as our East Coast train, which I joined at Edinburgh on Sunday evening, headed towards King's Cross.
We were running late after delays earlier in the journey, but only by a few minutes. The serious problems started near Finsbury Park station, in north London.
After being told there would be delays as we approached the station, we sat waiting for updates. They came every so often, but the announcer appeared to know little about when we would be up and running again.
The train wasn't excessively busy and people didn't seem angry - most people just seemed resigned to the situation.
We sat outside the station for well over an hour, eventually reaching King's Cross 90 minutes late - too late for the Underground and with long queues for taxis.
The problems were caused by overrunning engineering work at King's Cross, which are part of a £200m investment programme.
Transport Secretary Patrick McLoughlin said he would ask Network Rail what lessons could be learned from the episode. He urged affected passengers to claim their money back.
"Passengers are entitled to be reimbursed if they are delayed and train operators have compensation schemes in place, and I urge those affected by delays this weekend to claim.
"I expect every operator to be out there helping their customers receive the compensation they are entitled to as quickly as possible," he said.
On Saturday, Network Rail's managing director Robin Gisby apologised for the disruption, saying "we've let a lot of people down".
He defended the decisions that shut down King's Cross on Saturday and caused long queues at nearby Finsbury Park station, which passengers were advised to use instead.
He said engineers had worked "tirelessly" to complete the track replacement work.
The cancellations at King's Cross caused chaotic scenes at Finsbury Park, which then had to be temporarily closed following police advice.
Sara Nelson, from watchdog Passenger Focus, said the disruption was "extremely frustrating for passengers".
A spokesman for the Office of Rail Regulation said: "Network Rail, working with the rest of the industry, must learn lessons and prevent problems like this happening again."
Shadow transport secretary Michael Dugher said it was "unacceptable disruption, just as people try and get home after Christmas".