According to The Times, resources which were due to be placed onto drafting legislation to deal with exactly this kind of drone incursion were diverted instead to work on Brexit plans.
This year the Department for Transport quietly ditched plans for a draft bill aimed at controlling the use of drones and pioneering technology to prevent them from being used near airports. The legislation, which had been due for publication in the spring, was dropped amid pressures on the department, with civil servants diverted to work on Brexit.