The Government’s rail lifeboat is tracking up to six franchises amid fears operators could soon hand back the keys – putting a quarter of the train network at risk of renationalisation.

Officials from the Operator of Last Resort (OLR) are monitoring South Western, Transpennine Express, Northern, Southeastern, CrossCountry and c2c, industry sources have revealed. One senior insider said that the OLR is preparing for a surge in workload. Around 40 desks have been prepared on the eighth floor of the OLR’s Whitehall offices, they said.

The reasons for potential renationalisation vary. There are fears that South Western and Transpennine Express are struggling financially. They could end up in a similar situation to that on the East Coast main line, when Stagecoach handed back the network after racking up a £200m loss.

The prospect of Southeastern being put in public hands has risen after new Transport Secretary Grant Shapps last week scrapped a delayed tender for the vital rail artery linking Kent and Sussex with London.

A joint venture led by Go-Ahead has been given a contract extension until next April. Sources said Mr Shapps may be reticent to hand Go-Ahead a further extension after locking horns with the operator over services it runs on a different franchise that runs through his Hertfordshire constituency.

Northern has been hit by industrial action and delays. An auction of the CrossCountry network was shelved last year. It is understood that Essex network c2c, run by Italian train giant Trenitalia, is also being tracked.

A spokesman for Transpennine and South Western said: “It is quite normal for the Government to monitor and scrutinise all train operating companies, looking at a variety of factors.”

The operator will continue to operate them “according to their contractual terms”. All other operators declined to comment. The Department for Transport declined to comment.