Denis Tunnicliffe, the chief executive, admitted that the completion of the line had been jeopardised by an electricians' strike and "poor productivity" of the workforce. He was speaking amid warnings that outside staff could be brought in to break the strike, as industrial action went into its fourth day.
"Unless productivity improves we will not be able to finish the line in time. The present situation is very serious and sad," Mr Tunnicliffe said.
He told BBC's Radio 4 Today that he was "totally confident" the extension of the Tube line from central London to the dome in Greenwich, south- east London, would be finished, but only if the strike ended soon and if the workforce achieved "reasonable levels of productivity".
But representatives of the electricians said there was no question of work resuming until management addressed the health and safety issue at the heart of the dispute.Reuse content