Rail operator Southern’s franchise should face an independent Government-commissioned review as commuters continue to endure “appalling” disruption, according to a travel watchdog.

London TravelWatch today urged Govia Thameslink Railway (GTR), the company that runs Southern, to take up an offer from the Mayor of London to work with Transport for London to improve the service.

Last week GTR cut 341 trains a day in an “emergency” timetable, set to last at least four weeks, in a move it claimed would offer “greater certainty for commuters”.

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Stephen Locke, chair of London TravelWatch, said: “At the end of the four-week period, it is essential that the Department for Transport and Southern carry out a swift review of progress.

“If it is not possible to reinstate the 341 lost services at this point, they should take up the welcome offer from the Mayor of London to make Transport for London's (TfL) operational expertise available to help turn the service round.

“We would also like to see department ministers commit to an independent, objective review of how this appalling situation has come to pass.

“That means a close scrutiny of how the franchise was set up and how subsequent developments have been managed. Lessons must be learned so that future passenger interests can be properly safeguarded.

“Southern's passengers have suffered enough. The situation is urgent, and now is the time to make full use of the strategic agreement between the department and TfL announced earlier this year.”

In January the Government announced TfL would be taking over London’s entire suburban rail network by 2021.

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Mayor Sadiq Khan this week urged for Southern to lose its franchise sooner than planned, describing the company’s service an “embarrassment to our city”.

He added: “Notwithstanding the wider discussions on devolution, I now offer to go one step further and put my senior TfL team in charge of the GTR Southern franchise until we get a permanent resolution.”

A Southern spokesman said the company was working on improving its service for commuters and would not enter “arguments about political control”.

He said: “Last week, our revised timetable was delivering more punctual trains for the benefit of passengers with eight out of 10 trains arriving on time compared to just six out of 10 before it was introduced – and we put 16 services back in to the timetable where we could.

“But this week, our service has been hit hugely by issues outside our control, including overrunning engineering work on Monday, a deep hole caused by a collapsed sewer that closed all four main lines in and out of London Bridge on Monday evening and multiple signal failures.

“Right now, at GTR, all our focus is on resolving the immediate issues to restore the service that passengers rightly expect, not arguments about political control.”

The operator has been heavily criticised by MPs, some of whom have called for it to be stripped of its franchise with immediate effect, and has been slammed by passengers, who ranked Southern the worst in the country in a passenger survey published last month.

The Rail, Maritime and Transport union, which is embroiled in a bitter dispute with Southern over the roles of conductors, has called on the new transport secretary Chris Grayling to take urgent action over Govia’s “rock-bottom” performance.