Rail passengers are reporting delays and cancellations this morning after new timetables were introduced.
Govia Thameslink Railway (GTR) rescheduled every service on its Great Northern, Thameslink and Southern franchise as part of an overhaul billed as the biggest in the UK.
The operator apologised after it cancelled dozens of trains, hours after its new timetable began on Sunday.
It called the change a “significant logistical challenge”.
The Thameslink, Southern and Great Northern rail franchise includes services to Bedford, Luton, Peterborough, King’s Lynn, Cambridge, London King’s Cross, London Moorgate, Wimbledon and Brighton.
On Sunday, GTR apologised for “any inconvenience caused” to passengers but was unable to confirm how many trains had been cancelled.
A spokesman added: “We are introducing the biggest change to rail timetables in a generation and, as we have been informing passengers, we expect some disruption to services in the initial stages.
“This is a significant logistical challenge as we make rolling incremental changes across more than 3,000 daily services.”
He added the timetable changes would mean a 13% increase in services across the GTR network.
The RMT and Aslef unions said they understood the disruption was because there were not enough fully-trained drivers.
From Sunday, every schedule for Thameslink, Southern, Gatwick Express and Great Northern trains has been changed, in an attempt to improve efficiency.
It will mean 400 extra trains a day and new direct services from 80 stations into central London.
But passengers in a number of smaller locations complained they would be served with fewer or slower services.