Stan Herschel, regional organiser of the National Union of Rail, Maritime and Transport Work (RMT) has promised strike action if his demands are not met.

It follows an official announcement by Government minister Rosie Winterton that £300m will be invested into the Metro system.

However, this is dependent on 'market testing', which Mr Herschel claims is privatisation.

He said: "This will be a hell of a campaign – a battle royale on the industrial front.

"If our campaign to scrap this privatisation of the Metro system fails, then we'll be presenting a list of assurances required.

"If they are not met, then it is very likely that we will take industrial action in defence of our members' pay and conditions."

The conditions include no compulsory redundancies, the creation of a collective bargaining group for staff, employees, including new entrants, remain in current pension schemes, all staff travel facilities remain and staff number levels are guaranteed.

However, a Nexus spokesman said: "This is not privatisation, Nexus will continue to own all of the Metro, set fares and timetables, and make sure passengers have the best possible travelling environment.

"We've kept the RMT and our staff fully informed and we will continue to work with them on any issues they might have."

Mr Herschel added: "The Metro system is a successful public operation, and it should stay that way."