South Western Railway has been threatened with losing its franchise after the service was deemed "not sustainable in the long term".
The move follows its continued "poor operational performance" - including a £137 million loss.
Grant Shapps, the Secretary of State for Transport, said contingency measures were being drawn up as South Western Railway had not yet met their financial obligations.
It's hoped the measure will "ensure services that passengers depend on continue in any circumstance."
The Department of Transport is now looking at a number of options including:
- A new short-term contract with South Western Railway (SWR) - with tightly defined performance requirements.
- Transferring the operation into the public sector - known as the Operator of Last Resort (OLR).
South Western Railway operates routes connecting London Waterloo with Woking, Guildford, Reading, Bristol, Exeter, Southhampton, Portsmouth, Bournemouth and Weymouth.
Mr Shapps added that poor punctuality and reliability combined with slower revenue growth has led to the operator's financial performance being "significantly below expectation" since the franchise began in August 2017.
Industry figures show that, between December 8 and January 4, the proportion of scheduled train stops made within one minute of the timetable by SWR was 55%, compared with the average across Britain of 62%.
Members of the Rail, Maritime and Transport (RMT) union on SWR have staged a series of strikes stretching back more than two years in a dispute over guards on trains, which has caused travel misery for passengers.
The latest strikes lasted throughout December and into New Year's Day, leading to cancellations and delays.
The RMT has recently launched a fresh ballot of its members on continuing with industrial action.
Mr Shapps added his plans will not impact on the railway’s day-to-day operations.