Scottish ministers’ attempts to defeat wildlife crime are unravelling thanks to gamekeepers boycotting government meetings, and the abandonment of prosecutions over the apparent killing of birds of prey, according to wildlife campaigners.

The Sunday Herald can reveal that the Scottish Gamekeepers Association (SGA) has pulled out of meetings of the Partnership for Action Against Wildlife Crime in Scotland (PAWS) because it doesn’t trust wildlife campaigners.

We can also disclose that the Crown Office has decided not to begin proceedings on a case involving three allegedly poisoned buzzards on a Perthshire estate. This is the fourth case of alleged raptor persecution to be dropped in the last month. Between 2010-2015, 73 birds of prey were killed by poison alone in Scotland. In other cases, peregrines, hen harriers, buzzards, red kites and tawny owls have been shot since April 2014.

These new developments in the long and bitter battle over the illegal killings have put mounting pressure on ministers to get tougher. A petition to license game bird shooting is due to be considered by MSPs at Holyrood on Tuesday.

Wildlife campaigners say that licensing is now needed because the justice system is failing to protect birds of prey. Landowners, however, argue for more preventative measures and accuse campaigners of exaggerating the extent of raptor persecution.

Birds of prey are protected by law as they are endangered. But they can prey on grouse and reduce the numbers available to be shot by paying visitors to country estates.

PAWS was set up in its current form by Scottish ministers in 2009 to bring together stakeholders to tackle wildlife crime. But the SGA, which represents gamekeepers from estates across Scotland, has now decided to stop attending meetings.

SGA representatives say they will not turn up until methods of partnership working have been reviewed. Relations between the SGA and the Royal Society for the Protection of Birds (RSPB) on PAWS have become increasingly strained in recent months as each accused the other of wrongdoing.

“If the trust element is lacking, it makes it hard to sit around the table in a constructive way so hopefully these matters can be resolved,” an SGA spokesman said.

He stressed that SGA had not left PAWS, and would continue to work with the government and police.

RSPB Scotland stressed that it had tried for years to work collaboratively with SGA to prevent crimes against birds of prey. “Regrettably, their approach has repeatedly been to deny that these crimes are taking place, despite overwhelming evidence to the contrary,” said the group’s head of investigations, Ian Thomson.

“The SGA should consider very carefully what message their withdrawal sends out to the Scottish public about their real commitment to working with partners to stamp out the wildlife crime.”

In March the Scottish Parliament’s environment committee warned of “alarming mistrust” between SGA and RSPB Scotland. “PAWS has a crucial role to play in tackling wildlife crime,” said the committee’s convener, SNP MSP Graeme Dey.

“That’s why we must have greater partnership working between all organisations if we’re to see an end to the brutal killing and attacks against wildlife.”

The SNP’s former environment minister, Richard Lochhead MSP, pressed gamekeepers to go back to the table. “I'd urge the gamekeepers and everyone else to work with the partnership to be part of the solution,” he said.

The row comes against a background of rising concern about repeated failures to prosecute bird of prey cases. The Crown Office has recently dropped three cases. Now the Crown Office has rejected a police plea for prosecution after three allegedly poisoned buzzards were found at Edradynate estate near Aberfeldy in Perthshire.

The accused is understood to have left employment at Edradynate, but the collapse of the case has infuriated RSPB Scotland. “We are exceedingly frustrated and disappointed that again a case is not going to be tested in court,” said Thomson.

“This latest decision adds to our serious and growing concern that the justice system is failing Scotland’s birds of prey and strongly suggests that these laws are becoming impossible to enforce.”

The Crown Office stressed that it was committed to the rigorous, fair and independent prosecution of wildlife crime. It had to strike a balance between enabling justice and protecting the public from invasions of their liberties. Discussions with RSPB Scotland about the use of covert surveillance were continuing, said the Crown Office spokesman. “The Crown has consistently made clear the limitations which the law places on the admissibility of evidence which has been obtained irregularly.”

Holyrood’s environment committee is today writing to the Crown Office “seeking clarity on the use of video evidence in helping to bring alleged criminals to justice.” Lochhead is also meeting the environment minister Roseanna Cunningham on Wednesday, saying that “nothing should be ruled out at this stage” in the fight against wildlife crime.

According to the retired wildlife police officer, Alan Stewart, three previous cases had been abandoned because of the lack of evidence to identify of the culprit. “Identifying a person who sets out a poisoned bait is always extremely difficult,” he said.

“There must be another sanction against shooting estates and their employees where wildlife crime is clearly taking place. Licensing of shoots is the next clear step with licences being able to be withdrawn for a period of years.”

The Scottish Government is soon to publish a report on satellite-tagged birds of prey that have gone missing. “We will bring forward further measures to deal with wildlife crime when we judge it to be required, including, potentially, further regulation,” said a government spokesman.

Landowners highlighted criticisms of RSPB’s “unilateral covert surveillance” and the strict penalties that already exist for wildlife crime. “These should be complemented by increased preventative measures, education and training,” said David Johnstone, the chairman of Scottish Land and Estates.

“Preventative measures adopted widely by estates - such as stricter employment contracts and training regimes – have had a significant impact on the reduction of wildlife crime.”

Johnstone rejected an RSPB assertion that crime was endemic on sporting estates, arguing that it had declined in recent years.