RMT today said that it would do everything it could to prevent the line being offered as a "concession" by TfL, to a private-sector operator and would take steps to safeguard its members' jobs and conditions.

"The extension of the East London Line is a welcome boost for London, but there is no earthly reason why its operations should not remain within London Underground," RMT general secretary Bob Crow said.

"The private sector has already wreaked havoc on the Tube since its infrastructure was privatised, and they have been leeching £2 million a week out of the system in exchange for next to no improvements.

"Neither our members nor the vast majority of passengers who have experienced the disaster of rail privatisation would want to impose it anywhere else.

"Farming the East London Line out to the privateers can only mean further damaging fragmentation and the diversion of even more cash out of the system and into the pockets of privateers, and we will do everything we can to keep the operation public.

"RMT will take the necessary steps to safeguard the jobs, conditions and pensions of our members," Bob Crow said.