Quarter of drone users face £1000 fines
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Anyone who owns a drone weighing more than 250g must obtain an operator ID before their gadget is flown outdoors.
People who fly drones are also required to get a separate flyer ID by passing a theory test.
Registration became mandatory on November 29, but the Civil Aviation Authority (CAA) told the PA news agency just 75,000 drone users have submitted their details, out of an estimated total of up to 100,000.
Registration can be completed by visiting https://register-drones.caa.co.uk and costs £9 per drone owner.
The new rules were introduced as part of a crackdown on drone misuse.
In March, the drone no-fly zone around airports was extended from 1km (0.6 miles) to 5km (3.1 miles).
UK Airprox Board figures show there were 125 near-misses between drones and aircraft reported in 2018, up by more than a third from 93 the previous year.
Drone sightings at Gatwick in December 2018 caused about 1,000 flights to be cancelled or diverted over 36 hours, affecting more than 140,000 passengers in the run-up to Christmas.
A number of other airports have been forced to suspend flights for several hours due to drone activity this year, including Heathrow.
Department store John Lewis stopped selling drones in May because of the chaos they were causing at airports.
The CAA issued advice to people who receive drones as Christmas presents, to ensure they use their new gadgets safely.
In addition to registering their devices, users should read instructions relating to low power warnings and compass settings, to avoid a crash, which would be "an expensive first flight", the regulator said.
Among the key rules dictating where drones can be flown are remaining below 400ft (120 metres), keeping clear of aircraft and airfields, and not flying close to people or property.
Full details are in the CAA's code of conduct, named the Dronecode.
CAA assistant director Jonathan Nicholson said: "Getting a drone for Christmas is an exciting present, but drones aren't toys and we understand that you may be apprehensive about how and where to fly it.
"This is also the first Christmas that drone registration has been required. So, our short handy set of tips is designed to get you into the air and enjoying your new drone as quickly and safely as possible."