South Western Railway Watch, which is campaigning for improvements to the South Western Railway service, says that the next rail minister faces numerous challenges with the firm.
The news comes following the resignation of rail minister Jo Johnson, Boris' brother, last week.
Campaign co-ordinator Jeremy VarnsÂ said: '˜Following the resignation last week ofÂ Jo Johnson,Â passengers and campaigners will again be looking to the government to find the right person for the job following a succession of largely ineffective ministers.
'˜Top of the in-tray will be how to deal with under-performing operators such as South Western Railway, who have promised so much but continue to fail passengers each and every day.
'˜The lack of oversight and enforcement of contractual standards is something which undermines trust in the entire industry, as does the continuation of denying passengers competition.'
Mr Varns says that now is the perfect opportunity for the government to hold rail service providers to account.
He said: '˜If the government believes in the benefits of a privatised rail network, they must accept responsibility for making it work for the benefit of passengers and put measures in place to deliver a world-class network.
'˜Given the scale of the challenges which lay ahead, now is the time to install the best possible team at theÂ Department for Transport to give rail, and rail users, the priority and service they deserve.' Â