A new coordinated strike by train drivers of two unions threatens to disrupt the lives of millions of commuters.

Both Aslef and the Rail, Maritime and Transport (RMT) unions are balloting their members, claiming that industrial relations with Tube bosses have broken down.

But London Underground (LUL) said negotiations "have not even begun" in the dispute over issues ranging from health and safety to claims of harassment.

The latest threat follow two unrelated strikes by station staff earlier this month, which saw some stations close on New Year's Eve and January 9.

"These ballots are totally unnecessary," an LUL spokesman said.

"We are committed to working with all our trade unions to resolve the issues they are raising through consultation and negotiation.

"Given these negotiations have not even begun, we are surprised Aslef and RMT appear to be ignoring the agreed machinery of negotiation and have moved to ballot."

RMT general secretary Bob Crow accused Tube bosses of trying to force through new policies.

His union's ballot of 1,500 drivers will close on February 9, the same day as the Aslef vote.

"No doubt we will once more be accused of disruption but the blame once again lies squarely with management trying to impose rather than negotiate," Mr Crow added.