Govia Thameslink Railway, which also runs Southern, Gatwick Express and Great Northern services, introduced the changes on May 20 which were billed as adding almost an extra 400 trains across the network a day.
However a number of Thameslink services have been cancelled and GTR has introduced short-term timetable amendments meaning fewer trains are able to run across the Thameslink and Great Northern networks.
In a statement on its website GTR said: “We apologise to passengers for the continued disruption linked to the introduction of the new timetable.
“We are working on a recovery plan with rail industry partners.
“Meanwhile, as late notice changes continue to be made, we ask passengers to check train times on the day of travel using our service updates page. We expect disruption to ease over the coming month.”
In a letter to MPs, Transport Secretary Chris Grayling criticised the ‘wholly unsatisfactory levels of disruption on rail services following the huge timetable change last week’.
He said: “I am frustrated that what should have been a good news story for passengers, with the introduction of new services, new routes and expanded capacity has had such a poor start.
“The industry collectively has failed passengers.”
He added: “We were aware that there might be some disruption in the early days of any new timetable change of this size, but the scale of the problem has far outstripped any expectation.
“I am determined both that the problems are dealt with as quickly as possible, and that this is not repeated in the future.”
Have you been affected by cancellations and changes? Email the newsdesk.
To check for train times visit Thameslink’s website.