RMT is the Rail and Transport workers Union. Which driverless trains are there on the tube? Or you you mean DLR?
As to Driverless Tube trains.
https://www.wired.co.uk/article/driverless-tube-trains-tfl-boris-johnson
One example of these legacy complications is shared track between different lines and level crossings," she says. "This is the case on the oldest parts of the London Underground, where Victorian thrift led to the District, Metropolitan and Circle Line sharing track and running different routes. Another added complication is winding tunnels. Retrofitting any new system – take the example or new signalling to increase train frequency – is complicated and expensive."Those challenges mean that an entirely driverless Tube may be impossible if not just prohibitively expensive; no wonder then, that TfL says it hasn't even looked into the idea.