What is different about this dispute is that the two main unions, previously bitter rivals, have joined forces. The Tube has 3,000 drivers, with Aslef controlling two-thirds and the RMT the remainder. Virtually all drivers belong to one or other of the unions, and those who don't will, in the main, be too frightened to turn up for work and cross picket lines on strike days. Memories are long and any strikebreaker won't have an easy time even when the dispute is over. The unions will combine the strikes to take place on the same day.