Police are investigating allegations of illegal deer hunting in south-west England, following claims that a traditional hunt has been chasing stags with packs of hounds.

Investigators from the League Against Cruel Sports have passed a file to police with evidence they say shows that the Quantock Staghounds have broken the law.

Although the Hunting Act 2004 banned the hunting of foxes and wild mammals using dogs, hunting deer without hounds remains legal – deerstalking is said to be growing in popularity.

Three traditional hunts continue to chase deer on horseback in Somerset and Devon, helped by hunt followers and quadbikers, and they can involve as many as 400 people. The law allows hunters to use up to two dogs to locate wounded deer, to flush out prey from undergrowth, or for observation and scientific monitoring.

Packs of hounds can still take part in trail hunting, where a sample of animal scent – usually fox or deer urine – is dragged across the countryside for the dogs to follow. Anti-hunt campaigners claim this is often used as a cover for illegal hunting.

Volunteers from the league who monitor the three hunts say that one, the Quantock Staghounds, regularly takes a large pack of hounds to chase a stag and hinds. Darryl Cunnington, a retired police officer and league volunteer, said he had given wildlife officers at Avon and Somerset police a file of evidence from an incident on 22 January on the southern edge of the Quantock hills, near Bridgwater in Somerset. “Our evidence is that there were seven or eight hounds chasing deer across the moor,” he said. “We’ve identified the people involved. The hounds were not called off and may have been actively encouraged. We found no trail-laying and we think it shows clear illegal hunting.” Avon and Somerset police said inquiries were ongoing.

Nick Gibbon, chairman of the Quantock Staghounds, said: “If there [were] more than two hounds we would have been trail hunting. If hounds are seen to be hunting deer, they’re stopped. We’ve got a team of trail-layers that lays trails.”

Asked how it might be possible that the league had found no evidence of trail-laying, he said: “We film our trails being laid.”

A separate incident on 5 September 2016, captured on video by a league volunteer, shows at least six hounds chasing a deer in Willoughby Cleeve. The man who took the footage, Andy Kendall, also a retired police officer, said the stag escaped past a line of Quantock Staghounds supporters onto a sanctuary owned by the league.

Gibbon did not have any knowledge of the incident. “If a deer jumps up in front of them when they’re trail hunting, they’re stopped as quickly as possible,” he said. The Quantock Staghounds have about 12 or 14 hounds, he added. “We try to manage the deer on the hills within the law. We do do some trail hunting because we’ve got more hounds in the kennels that need to be exercised.”Previous attempts by the league to prosecute illegal hunting have been mixed. In 2013 a case against a Quantock Staghounds huntsman, Brian Palmer, was dropped for lack of evidence. In 2007, Richard Down and Adrian Pillivant were fined £500 each by Bristol magistrates for hunting deer with dogs .

The league estimates that around 200 deer are chased and killed every year, and it operates an Animal Crimewatch hotline, which received 66 reports of illegal deer hunting in 2017.

Hunters say they are helping control the deer population, which has doubled since 1999 to about 1.5m according to the Deer Initiative Partnership, a government-funded body, which believes culling some deer species may be necessary.

According to the Devon and Somerset Staghounds, which the league says has never been seen using more than two dogs at a time while hunting, the population of deer on Exmoor is at 2,500, compared with 75 when the hunt was founded in 1855.