Until a decade ago the Government just kept a secret list of teachers who were banned from working with children, but Labour established the Criminal Records Bureau to check if a wider range of people working with young or vulnerable people had any convictions that should disqualify them.
In the wake of the Soham murders, the system was expanded further through the setting up of the Independent Safeguarding Authority in 2009. Its officials were to keep a list of millions of employees and volunteers who had been cleared to work with children and would be able to consider unproven allegations made by managers, colleagues or members of the public.
Figures released under the Freedom of Information Act show that between January 2009 and February 2011, 13,486 cases were referred to the quango "for consideration under its discretionary powers". But only 557 - 4 per cent - led to the individual being barred.
Separate figures show that most of the referrals (2,186 in 2010-11) were made by care home or home help agencies, with a further 945 coming from local authorities, 513 from the education sector and 41 from faith groups.
One of those who found that his background was being scrutinised by the agency was the Rev Jeremy Hummerstone, who was the vicar of Torrington in Devon.
He had refused to undergo a Criminal Records Bureau check on the grounds that it was not part of the original conditions of his post, and was told by his diocesan safeguarding advisor that he had to be referred to the ISA for "persistently or recklessly" failing to comply with policies.
Mr Hummerstone paid £10 to see the ISA's file on him and discovered it included claims that he had written "inflammatory" comments about the child protection regime in his parish newsletter and on one occasion pinned up a Daily Telegraph article on the subject, as well as copies of private emails and reports of conversations.
He was eventually cleared by the ISA and has since moved to the diocese of York, where he agreed to have a CRB check as part of the conditions for a new job.
But he said he had been left scarred by fellow clergy acting like the "Witchfinder General" and reporting him for "thought crime".
Now 72, Mr Hummerstone said: "I thought someone had made an accusation against me, and I've seen careers ruined that way, but all it was was this refusal to take a CRB check.
"It seems to me that people can get quite a long way in making allegations before they're stopped, and it can do a lot of damage."
Amid public outcry at the scale of the original vetting scheme, which would have affected parents who set up a rota to take children home from after-school sports, it was first reviewed under Labour and then halted after the election so it could be returned to a "common sense" levels.
However the ISA is still operating and has now barred a total of 46,177 people from working with children, the vast majority because of relevant past convictions, while the investigation of allegations still takes place.
Under the new Protection of Freedoms Act 2012, the CRB and ISA will merge and a narrower range of people will need to be checked before they can work with children.
A spokesperson for the Independent Safeguarding Authority said that the discretionary barring system has helped ensure that "abusive care workers are not able to move jobs and harm elderly patients again", for example.
He added: "Our work in assessing referrals plays a key role in safeguarding vulnerable groups including children - as does our decision-making work with automatic barring cases."
