Police on Merseyside have had to ground their new drone over concerns it was being used illegally without a licence.
Merseyside Police said they had been unaware they needed a licence to fly the remote control helicopter, which is fitted with CCTV.
The Civil Aviation Authority (CAA) said it needed to be consulted over any use of the drones, that can fly up to 400ft and reach speeds of 30mph.
The force's drone was used last week to catch a car thief in thick undergrowth.
All unmanned aircraft, not just ones that weigh 15lb (7kg) or more, now have to be licensed to conduct aerial surveillance work after the law changed at the start of the year.
They need CAA permission to fly within 164ft (50m) of people and within 492ft (150m) of buildings.
The CAA said any breach in regulations, which came into force on 1 January 2010, would be "treated seriously".
A Merseyside Police spokesman said: "Since the force has known of the change in regulations all Unmanned Aerial Systems (UAS) flights have been suspended and will remain so until the appropriate licence has been granted."
He added that the CAA had been invited to inspect the drone and see how they used it.
The air space regulator confirmed it was investigating the use of the drone by Merseyside Police and the force had stopped all drone operations.
A CAA spokesman said it had the powers to fine those who operated illegally, but said the investigation with the Merseyside force was only in its early stages.
The military-designed equipment is directed through a remote control, which is used by an officer on the ground.
The police force has had the drone since November and has said it could be used for a range of uses, from hostage situations to monitoring large public events.
Last week, officers said thermal images provided by the force's drone led it to the first arrest it had been involved with.
A man was tracked down with the camera after he ran off from a stolen car.
The technology onboard the drone meant the officer using it was able to use live images of the suspect's body heat. The officer then directed patrols on the ground to where the man was hiding in undergrowth.
Two men were arrested and later bailed in connection to the theft.