A potential cull of the largest owl in Europe has placed the government at the centre of an increasingly bitter row between conservation groups.

There are fears that the eagle owl, a non-native species seen in growing numbers in the British Isles, poses a serious threat to established wildlife. Some groups say the formidable predator must be protected. Others claim it could disturb the UK's existing wildlife balance and, as a non-native species, should not be afforded protection.

The owl, which has a wing span of up to 3ft, is found in much of northern Europe and Asia, but many experts question whether it was ever a native species in the UK. It will swoop on pheasant, young deer and rabbits, but there are concerns it poses a particular threat to other birds, particularly hen harriers.

"We don't want the population to grow any larger," said Grahame Madge of the Royal Society for the Protection of Birds. "There is no suggestion they are causing a problem right now, but the introduction of a large non-native predator has the potential to cause problems in the future. There is a need to strike a delicate balance."

An alternative option to a cull would be for owls to be captured. But this is unlikely to be well received by conservation groups which claim fossil evidence suggests the bird was once native within the British Isles.

Gauging how many eagle owls may be at large in the UK – and, therefore, the potential threat they pose to indigenous species – is difficult. Some experts estimate there could be as few as 20 pairs of wild birds.

"We don't have a handle on how many there are," said Madge, who is sceptical about claims the owl was once native to Britain. "If it had once lived here, you would expect to find it recorded in folklore and this does not appear to be the case. Nor is it likely that the bird travelled here from Holland or Belgium because the eagle owl doesn't like flying long distances over water."

Experts agree, however, that the bird, which is easy to breed, is becoming increasingly popular among falconry enthusiasts with the result that a rising number are escaping into the wild.

"A number of eagle owls have escaped," Madge said. "Perhaps some owners have not looked after them properly and these birds are forming a small but growing population in the wild."

The environment minister, Richard Benyon, confirmed in a statement to parliament this month that his department's officials had held discussions with conservation groups about how to restrict the spread of the owl.

While Benyon acknowledged no "immediate action is needed to control them", he confirmed that a cull of the birds was a possibility as the government was continuing "to monitor the effect they are having and will reassess the situation if necessary".

For now, the government has backed plans put forward by the RSPB, which has called for further evidence of the owl's impact on other species coupled with a new awareness campaign warning owners about the unlawful release of eagle owls.

The World Owl Trust claims the eagle owl should be protected by the European Union birds directive and has warned it will take legal action if a cull is sanctioned. But because many of the birds are considered to have escaped and are therefore non-native, some experts say the owl is not entitled to protection.

There is speculation that some of the owls may have escaped from hunts. About 20 hunts bought golden eagles and eagle owls in an attempt to bypass the 2004 Hunting Act that permits dogs to flush out wild mammals for a bird of prey to hunt.

There are fears the birds could start to breed, significantly increasing their numbers in the wild, but there is little evidence to support this concern.

A government risk assessment, published earlier this year, concluded that an increasing population of eagle owls in Britain would pose a significant threat to several species including hen harriers, which are already at risk of being shot and poisoned because of the threat they pose to game birds.

Evidence of the danger eagle owls pose to hen harriers is contentious. In June, Natural England and the RSPB reported that an eagle owl in Bowland, Lancashire, a popular spot for the birds, had been filmed attacking a nesting female hen harrier. However, the World Owl Trust has questioned the veracity of this claim and called for the footage to be released.

There are concerns that some people will take the law into their own hands if an increase in the number of eagle owls is not addressed. In 2006, a female owl in North Yorkshire that had produced 23 chicks in 10 years was shot and killed.