One of Britain's biggest online paedophile inquiries is to be challenged in the court of appeal amid allegations from campaigners that hundreds of men have been wrongly convicted in a mass miscarriage of justice.

For more than two years a small group of experts have claimed that Operation Ore, the police inquiry into thousands of British men, was tainted because the database at the centre of the investigation contained evidence of widespread credit card fraud. Their allegations will be tested for the first time in the appeal court within weeks, when a judge examines a test case that could expose a huge miscarriage of justice, lawyers say.

The single judge will decide whether the case should go to a full appeal.

Chris Saltrese, the solicitor representing the convicted man, Anthony O'Shea, said: "If his appeal is successful the convictions of others for the same offence will fall too. We are talking in the hundreds and we say this is a huge miscarriage of justice."

An estimated 39 men have killed themselves as a result of being arrested and prosecuted during the Ore inquiry, and the details of every individual who was convicted or cautioned have been placed on the sex offenders register.

Senior officers in Ceop, the child exploitation and online protection unit, who co-ordinated the inquiry, have been anticipating the test case for some time. They are adamant that Ore was an extremely successful operation, which led to more than 2,600 British men who downloaded images of child abuse, or attempted to, being brought to justice. The vast majority of them pleaded guilty.

Operation Ore began in 2001 after the conviction in America of a couple behind Landslide Inc, an online trading company that provided access to adult pornography and child abuse images.

US investigators passed the names of 7,100 Britons on the Landslide database to the national criminal intelligence service, a forerunner of Ceop.

The last prosecutions in Ore took place earlier this year.

O'Shea's case is one of an estimated 200 or more involving men who were convicted of incitement to distribute indecent images of children. A father of two, he was jailed for five months in 2005 for two counts of incitement to distribute indecent photographs of children and three of attempted incitement to distribute indecent images. A lesser charge than possession, incitement was used in those cases where someone's details were on the Landslide database but there were no images found on the suspect's computer or in his home.

O'Shea's home was raided in 2002 but no images were found. Saltrese said his case was that he accessed adult pornography but that his legal team would produce evidence that his credit card had been fraudulently used to access a paedophile site within Landslide.

At the time the card was used O'Shea was at a festival in the south-west of England, Saltrese said.

Ceop says its figures suggest that 161 individuals were convicted of incitement, with 68% pleading guilty. But Saltrese, who represents dozens of those convicted, believes the figure could be much higher. A separate campaign group says that it is dealing with the cases of more than 80 men.

"I have clients who have lost everything: their jobs, their homes, their marriages, their children and their health," Saltrese said.

He and his experts have been able to get a copy of the Landslide database – which was never disclosed in full to the defence teams in Ore cases.

"It is absolutely riddled with fraud," he said. "We are not just talking about isolated incidents here. In some cases clients did make a complaint to their credit card companies that they had been the victims of fraud, in others they didn't, but that is kind of by the by – even if they hadn't made a complaint we say the evidence against them is unreliable."

But other experts who worked closely with the police during the Ore inquiry and with defence teams strongly dispute the case put by Saltrese and his team.

Professor Peter Sommer, a leading expert in computer crime, said: "There were very high levels of correlation between people having subscribed to that website and people being found in possession with child abuse images.

"In the incitement cases they did not just use the details on the database as a reason to prosecute. They went to the individual's bank to confirm that transactions had taken place, they checked whether the individual had ever complained that his card had been used fraudulently. They did not charge everyone they investigated."

He said that although the defence teams were not allowed access to the whole database, experts had been given access to parts of it. "I am not saying there may not be individual cases where the convictions might be unsafe but to say there was widespread fraud and a widespread miscarriage of justice does not to my mind stand up."

Brian Underhill, the computer expert who travelled to America to copy the Landslide database for the police as part of the Ore inquiry, told the Guardian: "It's been two years since the allegation of widespread credit card fraud was put forward and I have yet to see a fragment of tangible evidence to support the allegation."

Ceop said that Operation Ore had involved an unprecedented number of cases, each of which was tested several times to ensure the validity of the intelligence and evidence before a prosecution was brought.

It said in a statement: "No evidence of widespread or endemic fraud has ever been found in relation to cases pursued to prosecution as part of Operation Ore. The veracity of any evidence to contradict this should be tested in the criminal justice environment.

"To the best of our knowledge all incitement cases included additional evidence to support the prosecution beyond simple, single credit card details.

"At the time of Operation Ore, individuals were suspected of subscribing to a website offering child abuse images. Those who had would have provided personal data to a registration page ... name, postal address, email address, a personal password and their credit card details ... The IP address of the subscriber may have been captured by the system.

"We would have expected that once a defendant had raised the possibility of being a victim of credit card fraud, inquiries would be undertaken in order to ascertain if that was correct."