The layer split doing all the work. You don't go from TfL licenses passenger services to the Department issues permits unless someone decided claiming local consent costs less than explaining why the governance was always whoever owns the permit owns the veto and the regulation was the designed gap.
Under current rules, TfL licenses passenger services, but the government decides whether autonomous vehicles can operate. As it stands, when it comes to fully autonomous passenger services, the Department for Transport would issue permits for robotaxis with TfL only able to grant or refuse consent, rather than regulate their usage on London's streets.



