London Mayor Sadiq Khan has stepped up efforts to take control of Southern Rail services amid union claims that passengers and staff were being "held hostage" because of delays and disruption.

Mr Khan said he urgently wants to put a Transport for London team in charge of Southern's services until the Government resolves staffing and industrial relations problems.

The company, owned by Govia Thameslink Railway (GTR), has cut 341 services from its timetable following weeks of problems caused by staff shortages, increased sickness levels and industrial action over plans to change the role of conductors.

In a letter to new Transport Secretary Chris Grayling, the Mayor said: "Thousands of Londoners and longer-distance commuters simply cannot get to and from work, and are understandably furious.

"There is no doubt that the franchise must now be in default, and I have previously called for your Department to step in and take control.

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

Meanwhile, the Rail, Maritime and Transport union (RMT) said passengers and staff were being "held hostage" as Brighton Station closed last night due to overcrowding

Services continue to be "plagued" by delays, cancellations and short train formations across the franchise, said the union.

General secretary Mick Cash said: "The situation has now moved from chaotic to downright dangerous, and the continuing attempts to blame that on the front line staff by the company bosses is outrageous.

"Passengers and staff alike are being held hostage by this failed rail operation and the silence from the new team at the DfT is deafening.

"There has to be urgent action to remove GTR and bring in Directly Operated Railways before there is a major disaster. "

Liberal Democrat London Assembly transport spokeswoman Caroline Pidgeon said: "As a daily user of Southern Rail I am painfully aware of its appalling service that has been provided over many months.

"Fundamental errors have been made in terms of planning by its senior management.

"The permanent solution must be stripping out much of the franchise from Govia and running it by London Overground.

"In the short term the company needs to state when their reduced timetable will come to an end. The company also needs to come clean as to how many drivers they actually require to run their full timetable without relying on the use of overtime and set out their exact plans to address their driver shortage."

Labour's transport spokeswoman on the Assembly, Florence Eshalomi, said: "The Government's weak approach to tackling Southern over their staffing issues and sub-standard performance has left passengers in purgatory.

"A TfL takeover is a sensible step towards addressing the problems plaguing Southern, which the Government have so far been content to kick into the long grass."