Perhaps the hardest thing for Jim Bates to hear at his sentencing for making false written witness statements in criminal proceedings was the Judge, Simon Hammond, saying: "I’m quite sure his career as an expert witness is now finished."

Bates is a founding father of the UK's forensic computing industry. He made his name analysing the Aids Trojan back in 1989, and had then been invited to lecture at the Police Bramshill Training College in Hampshire on the emerging threat of viruses. His forensic expertise has been used in major cases ever since.

Waiting for more than four hours for sentencing outside Court 4 at Leicester Crown Court yesterday, Bates had been mulling over his future. It was not about would he go to prison like fellow perjurers Jeffrey Archer and Jonathan Aitkin, but what would the Judge say about his lifetime’s work. And how could he continue his 'calling' as his brother Don called it.

"I hope they re-open the cases," said Bates. That would just confirm his legacy, but how could he continue his work exposing flaws in Operation Ore, the police investigation into UK users of a US-based site that sold images and video clips of child porn.

"It’s a niche. It's not rocket science, but I’m good at it," he said. His crime had been to say he had a BSc degree in electronic engineering, in Court and on witness statements on five occasions between 1995 and 1997, when he didn’t.

He was sentenced to six months for each of the four counts of making false witness statements, and one count of perjury, suspended for two years. He also has to pay £1,000 towards costs.

In his pre-sentence summing up Judge Hammond said: "There is no doubt as to his expertise. He was no charlatan… His experience was sufficient to justify his status… he provided invaluable assistance to the police.

"This is a very sad case. It is very important that an expert witness must be scrupulously honest. It was absolutely wrong to claim he had a BSc when he hadn't."

The leading names in UK computer forensics tend to be academics: Professor Tony Sammes who set up the Centre for Forensic Computing at Cranfield University, Professor Peter Sommer at the LSE, Professor Neil Barrett who lectures at Cranfield and works for the EU.

"I should have got some formal qualifications in computer forensics? They didn’t exist and in spite of Tony Sammes they still doesn’t exist," said Bates.

"You have to allow for people who don't have academic qualifications or the whole thing becomes enthralled to academe."

So why lie? He says he was encouraged by police officers to give himself some credibility. He had told the Court he’d paid £50 to take some exams to give him the equivalent of a BSc. Judge Hammond called this a "bluff" and "a lie".

Bates is often critical of his rivals and through his career has written exactly what he thought on his websites. But in his own address to the court he referred to Sammes' work assessing his own.

Bates had worked as the defence expert for Detective Constable Brian Stevens, the police family liaison officer attached to the family of one of the murdered Soham schoolgirls Holly Wells and Jessica Chapman. Stevens was arrested as part of Operation Ore on charges of possessing child pornography.

The case was dropped after Bates' work led prosecution lawyers to admit that their expert witness had made "substantial errors" and reached a "wholly false" conclusion in his analysis of the officer's laptop computer. Stevens was later jailed for falsifying his alibi to escape the charges.

In court Bates revealed that Sammes, "the foremost computer expert in the cou ntry", had reviewed the prosecution and defence work on instructions from the Crown Prosecution Service.

"My work was unimpeached in the professor's report."

Judge Hammond agreed. "Professor Sammes checked the defendant's work and concluded he was right in his conclusions," he said.

But Operation Ore has been exposed to be flawed thanks to Bates work. He estimates that between 50 per cent to 80 per cent of the people caught up in it are victims of credit card fraud. In all, 7,272 British residents were on its target lists, more than 2,000 of whom have never been investigated; and 39 men have killed themselves under the pressure of the investigations.

Bates is passionate about helping those wrongly accused in this case. One man caught up in the case, who Bates had helped, was at Bates side supporting him at Leicester Crown Court.

Bates, who defended himself after sacking his legal aid team, now lives on a state pension with his wife, in rented accommodation. He is investigating whether he has grounds to appeal his conviction.

Don Bates, Jim’s younger brother, said: "He genuinely believes his education is to that level. I think they're going after him for something, anything, because of the comments on his website. I’ve been very proud of some of the things he's done. He’s one of the good guys."