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Passengers are to be hit tomorrow by a District line walk-out over a Tube driver alleged to have passed three red signals in his 11 weeks driving.

He had been qualified for 18 weeks but due to sickness, retraining and a compulsory removal from duty only drove for 11, London Underground claims. Two of the signals passed at danger (spads) were within a four-week period.

Nigel Holness, director of network operations at London Underground (LU), said it was “simply not safe for this employee to continue in a role as a driver”. LU refused to identify the severity of the spads — which could derail a train — or where they took place.

After the first incident he spent three days retraining with a driver/instructor in the cab. After the second he spent five days retraining and another five on stand-down. After the third spad he was removed from driving duty.

The District line is the busiest on the network and used by more than 800,000 passengers a day.

Services will not come to a halt but severe disruption is forecast — particularly in outer London areas. Aslef is the main drivers’ union but driver members of the RMT, not involved in the dispute, could refuse to cross picket lines, adding to the disruption.

Other Tube lines will operate as normal though the Circle line, which doubles-up for parts of the District line, will be much more crowded than usual.

Faces of frustration: Battling the Tube strike 17 show all Faces of frustration: Battling the Tube strike 1/17 A tired commuter sits on a bus at Liverpool Street Jeremy Selwyn 2/17 A man looks through window on a bus at Victoria Station Carl Court/Getty Images 3/17 The top deck of a bus full on unimpressed commuters Stefan Rousseau/PA 4/17 Commuters queue patiently at Victoria bus station Justin Tallis/AFP/Getty Images 5/17 A man yawns on his way to work, as extra buses are laid on to help with capacity during a 24-hour tube strike Justin Tallis/AFP/Getty Images 6/17 Unhappy commuters on a bus at Victoria Station Alex Lentati 7/17 A man looks out on a window on a bus whilst battling the 24 hour tube strike Stefan Rousseau/PA 8/17 Commuters in Stratford, London wait for buses Stefan Rousseau/PA 9/17 A bus loaded with passengers bear the brunt on London Underground industrial action PAJohn Stillwell/PA 10/17 Disgruntled commuters walk across London Bridge making their way to work on foot Leon Neal/Getty Images 11/17 Commuters are seen through the windows of extra buses AFP/Getty Images 12/17 Bus queues at Liverpool Street Jeremy Selwyn 13/17 A woman wait for a bus at Liverpool Street Jeremy Selwyn 14/17 Commuters are seen through the windows of extra buses Justin Tallis/AFP/Getty Images 15/17 A woman make a call on her phone during the tube strike Jeremy Selwyn 16/17 Commuters queue for busses at Victoria Station Carl Court/Getty Images 17/17 People queue for buses at London's Waterloo Station Dominic Lipinski/PA 1/17 A tired commuter sits on a bus at Liverpool Street Jeremy Selwyn 2/17 A man looks through window on a bus at Victoria Station Carl Court/Getty Images 3/17 The top deck of a bus full on unimpressed commuters Stefan Rousseau/PA 4/17 Commuters queue patiently at Victoria bus station Justin Tallis/AFP/Getty Images 5/17 A man yawns on his way to work, as extra buses are laid on to help with capacity during a 24-hour tube strike Justin Tallis/AFP/Getty Images 6/17 Unhappy commuters on a bus at Victoria Station Alex Lentati 7/17 A man looks out on a window on a bus whilst battling the 24 hour tube strike Stefan Rousseau/PA 8/17 Commuters in Stratford, London wait for buses Stefan Rousseau/PA 9/17 A bus loaded with passengers bear the brunt on London Underground industrial action PAJohn Stillwell/PA 10/17 Disgruntled commuters walk across London Bridge making their way to work on foot Leon Neal/Getty Images 11/17 Commuters are seen through the windows of extra buses AFP/Getty Images 12/17 Bus queues at Liverpool Street Jeremy Selwyn 13/17 A woman wait for a bus at Liverpool Street Jeremy Selwyn 14/17 Commuters are seen through the windows of extra buses Justin Tallis/AFP/Getty Images 15/17 A woman make a call on her phone during the tube strike Jeremy Selwyn 16/17 Commuters queue for busses at Victoria Station Carl Court/Getty Images 17/17 People queue for buses at London's Waterloo Station Dominic Lipinski/PA

Passengers were warned of “delays to all journeys throughout the day.”

The driver has been transferred to station duties by “mutual” decision, said LU — a claim robustly denied by union bosses. Finn Brennan, Aslef organiser on the Underground, said the only reason the driver had accepted a transfer of duty was because LU had threatened disciplinary proceedings if he did not. LU denies taking disciplinary action.