Two military drones are crashing every month on average, according to research that raises questions about the safety of the technology, both in conflict zones and civilian environments.

Accidents Will Happen, a report published by the campaign group Drone Wars UK, reveals that there have been more than 250 crashes involving the large unmanned aircraft in the past decade. A Reaper drone has a maximum speed of 480kph, a range of 1,800km and is armed with up to four missiles and two 230kg bombs.

The Ministry of Defence and industry lobbyists are pushing regulators to open up British airspace to a new drone called the Protector.

Out of the 254 crashes detailed in the report, 178, or 70%, of them were drones being operated by the US military. The vast majority of these were manufactured by General Atomics, which makes the Predator. British-operated drones were involved in 14 of the crashes.

The causes of around half of the crashes – compiled from official air force inquiries, freedom of information requests and press reports – include mechanical failure, communications problems, engine failure and pilot error. Almost two-thirds, or 64%, occurred while the drone was in mid-flight, while 28% occurred at either take-off or landing.

The MoD wants to fly the new Protector drone within Britain for training purposes as well as for what it calls “homeland defence tasks”.

But critics question whether this may put civilians at risk. “Pressure from lobbyists to open up our skies to these large drones is mounting,” said Chris Cole, director of Drone Wars and the report’s author. “However, the technology is far from mature and, as the data demonstrates, accidents occur frequently.

“The rise in the use of military unmanned systems is dangerous for a whole host of reasons, and this push to introduce them into UK airspace not only normalises their use but may well also put the safety of the British public at risk.”

Amazon announced last week that it will use small drones to deliver packages to customers in the United States “within months”. They will apparently be able to travel up to 15 miles and carry packages weighing up to 2.3kg.