Seven people were taken to hospital after the Camden crash

The Edgware branch of the Northern Line - between Golders Green and Charing Cross - is running through Camden Town and Charing Cross.

But they are at reduced frequency and stopped at 0915 GMT to allow further engineering work.

Passengers will have to use replacement buses and they are being told to allow more time for their journeys.

The East Finchley to Euston section remains closed after services were suspended on the whole line following the derailment on 19 October at Camden Town, north London, which injured seven people.

London Underground's (LU) managing director Tim O'Toole said: "I'm sorry this has taken longer than expected, but we had to be assured that this section of line was safe to reopen before we started to run trains again.

Strike action

"I hope we will have a Northern Line service to all stations soon, though the extent of the damage caused by the derailment means we won't be able to return to the previous level of service immediately."

Tube Lines, the consortium in charge of maintenance on the line, is still trying to find out why the accident happened.

It was the second derailment inside 48 hours and union leaders are now pressing ahead with plans to ballot Tube workers for a strike over safety.

On 17 October a Piccadilly Line train derailed at Hammersmith in west London.

Crisis talks

Crisis talks were held between representatives of the Rail, Maritime and Transport union (RMT) and managers on Tuesday aimed at preventing industrial action.

But union leaders say they "heard nothing" to stop them balloting members over industrial action.

The RMT union opposed the privatisation of Tube maintenance on safety grounds and wants it to be returned to LU.

Ballot papers are due to go out this week to RMT members over possible strikes and "go slows" in the run-up to Christmas.