Strike action on some of the busiest railway lines into London has begun after talks failed between unions and National Express.
It is the third 48-hour strike to affect trains between London and Essex, Norfolk, Suffolk and Cambridgeshire,
A spokesman for Aslef said the union's executive had also decided to call a full week of strike action next month.
The action is by members of Aslef, the RMT union and the Transport Salaried Staffs' Association (TSSA).
It started at 0001 Thursday and will end at 2359 BST on Friday.
National Express East Anglia said "most services will not run" adding that any trains which did run were expected to be "extremely busy".
The dispute is over pay and condition.