A rail line used by thousands of City workers which reopened yesterday after a for a £40 million upgrade was suspended during this morning's rush hour because of signal failure and a stalled train.

The Waterloo and City line, which runs from London's Waterloo station to the City, experienced signal problems from 7.30am.

A stalled train later caused another suspension of services on the line, known as the Drain, and used by 37,000 passengers a day.

The line was upgraded by Metronet, which had said it was due to reopen on September 1 after a five-month closure .

Tim O'Toole, managing director of London Underground, said: "Following any closure for engineering works, especially a long-term closure, it is important that the line is reliable when it reopens.

"We are demanding that Metronet addresses this issue immediately and ensure that the signal failures do not persist."