The DfT said in a statement on Wednesday that while SWR had not yet failed to meet financial commitments, its performance was such that the government was working on contingency measures.

Those could include either a new short-term contract with the current operators or nationalisation, through transferring the running of the network to the government-owned Operator of Last Resort.

The dire situation at SWR, which connects southern England to London, comes at a time of wider problems within Britain's privatised rail system, following the failure of several high-profile rail contracts and amid consumer complaints over strikes and poor service.

SWR is currently operated by listed UK transport group FirstGroup and Hong Kong's MTR.

An independent review into how Britain's privatised rail network should be run in future headed by former British Airways CEO Keith Williams is due in the coming weeks.

(Reporting by Sarah Young; editing by Kate Holton)