Countryside groups have called for tougher rules on the use of tracking devices after a huntswoman allegedly caught an anti-hunt activist planting one under her horse trailer.
The incident has prompted calls for the Home Office to close a loophole in the law after it emerged that the activist is to face no charges over the incident
Hunt supporters fear that could appear to give the green light to anyone to install a tracker on another person's car without consent and escape criminal prosecution.
Trackers are now easily available, cheap, and are used lawfully with the owner’s permission for tagging expensive cars, pets and even newly qualified young drivers.
But there is potential for more sinister purposes to spy on individuals and find out their movements.
The legal loophole was identified after Mary Wynne-Jones, 68, from Market Drayton, interrupted a hunt monitor she claims was trying to fix a tracker to her Land Rover and trailer on her return from riding with the Wynnstay Hunt, which straddles the Cheshire and North Wales border, on December 6 last year.
The woman claimed she was thinking about buying a trailer and wanted to see if she could manage one, before driving away.
But after inspecting her vehicle Mrs Wynne-Jones discovered a tracker in the chassis of the trailer and called the police.
The female suspect then returned unexpectedly and is said to have admitted to Mrs Wynne-Jones and two police officers that she had placed the tracker.
Mrs Wynne-Jones said: " She told me it was uncharacteristic and a spur of the moment thing."
But shortly before Christmas Mrs Wynne-Jones received a letter from North Wales Police stating: "As the female made it quite clear the alleged tracker was NOT placed there to commit theft, no crime has been committed."
PC Perrin, of Rhos police station, who wrote the letter, added that various other offences had been considered "but these circumstances did not fit any."
She disclosed however that details of the suspect and her vehicle had been circulated to officers from North Wales and Cheshire forces for future monitoring.
Mrs Wynne-Jones said" I really cannot believe this. I think it has to be an illegal act for someone to put a tracker on someone's vehicle without their consent.
“It was obviously intended to follow me so saboteurs could find out where I was going hunting which is a legal activity. This should be a criminal offence."
The woman identified by Mrs Wynne-Jones as allegedly planting the tracker denied doing so, but admitted to the Telegraph that she had considered such a course of action.
Speaking at her home the woman said: “I have thought about tracking – I’ve looked into it. It’s something we have considered. I honestly don’t know whether tracking a car is illegal. I think it’s a bit of a grey area. But I haven’t done it and I’m not aware of anyone who has.”
The 73 -year-old, who belongs to the Cheshire Monitors – which tries to expose illegal hunting in the county - added: “For us it’s about finding the hunts that are hunting illegally. 85 percent of the population don’t want fox hunting. People like it less and less – they have the hunts coming on to their private land and going into their villages and they don’t want them.
“The problem is that the 2004 Hunting Act has a lot of loopholes and they exploit them to the maximum.”
Trackers have been previously spotted on vehicles of hunt supporters and marksmen involved in the official badger cull, but this is thought to be the first time an alleged perpetrator has been caught in the act.
Tim Bonner, chief executive of the Countryside Alliance, who is contacting Home Secretary Priti Patel about the legal loophole, described the episode as "incredibly sinister and worrying."
He said: "The repercussions go way beyond hunting. It is concerning that anyone could so easily be the victim of stalking. Most would agree this is a shocking violation of privacy which could put people in serious danger. Action needs to take place to address what looks like an unacceptable loophole."
North Wales Police declined to comment on a specific case but said in a statement: " A private individual placing a tracker on another person's vehicle is not in itself a criminal offence.
"However a course of such conduct may constitute a criminal offence in certain circumstances. If damage is caused or there is an intention to steal the vehicle, they would also be criminal offences."
Lawyers believe the criminal law has not caught up with the use of GPS trackers in Britain.
Rupert Jones, a criminal barrister in Birmingham, said: "There is definitely a gap in the law. The vehicle interference offence only applies when the intention of the installer is that the car is to be stolen.
“The concerning situations are when someone installs a tracker to work out where someone lives, or what their daily habits are, with an intention of committing another offence against them or their property."
Nicholas Hall, a criminal barrister in London, said: "Given the increasing popularity of trackers, it may be new laws will be introduced in future to capture this specific type of behaviour."
The Home Office declined to comment.