Sir Roger Singleton launched revised rules for adults who work with children
The number of people to be vetted to work with children will increase beyond the estimated nine million, says the safeguarding authority head.
Sir Roger Singleton, speaking after the launch of revised child safety rules, accepted it was likely that the total of registrations would rise further.
After pressure from head teachers' leaders the government has narrowed the range of the vetting scheme.
Children's Secretary Ed Balls says he wants to find a "consensus" on safety.
Although the revised rules have been announced as a reduction in the people who will need to be vetted, the registration list is set to increase each year - with more people being added than are likely to leave.
As such this child protection database, already the biggest of its kind, will cover even more of the population.
"We don't have a prediction for how many will be on it," said a Home Office spokesman.
The revised rules for England, Wales and Northern Ireland launched on Monday have been intended in part to reduce the number of people who will need to be vetted by the Independent Safeguarding Authority.
VETTING AND BARRING
People who have regular, frequent or intensive access to children have to register with the ISA
It costs £64 to register, but volunteers have their fees waived
The ISA is being phased in across England, Wales and Northern Ireland
Individuals will be able to apply to register from July 2010. It will be mandatory from November 2010
The scheme covers England, Wales and Northern Ireland
A separate but aligned scheme is to be introduced in Scotland
There had been plans for some 11.3 million adults to be vetted - but after criticism from school leaders and children's authors the rules on frequency of contact have been eased, reducing this to an estimated nine million.
The amount of contact needed with children before an adult needs to be vetted, in a workplace or voluntary setting, has been changed to at least once a week.
And groups such as foreign exchange students are no longer covered by the vetting scheme.
But Sir Roger accepted that in the longer term the database of registrations would increase rather than reduce.
Registration with the Independent Safeguarding Authority is for life - so when people cease to volunteer, change jobs or children grow up and parents end their involvement in clubs, they will remain on the vetting database, unless they actively ask to be removed.
Each new intake of volunteers or people starting jobs that require vetting will then add cumulatively to the total - with no number set for an upper limit.
At a briefing to introduce the revised regulations, Mr Balls challenged the spreading of ungrounded fears about the vetting scheme and said there had been "wild allegations" about what would be required.
He said it would be "ludicrous" for a school to expect all visitors to have undergone a criminal records check.
Mr Balls stressed that the vetting plans were not about private arrangements between parents, but were about staff and volunteers organised by schools and clubs.
Sir Roger also criticised organisations which had been "over-zealous" in their interpretation of child protection rules.
But he also said there was "continuing concern" over the lack of checks on people from overseas who were now working or volunteering in the UK.
The chair of the safeguarding body spoke of the need to find a balance between the need to protect children and to ensure that adults are not unjustly barred from working.
Along with convictions and cautions, case workers at the Independent Safeguarding Authority will have to decide on the significance of "soft" intelligence, which might not have prompted any legal action in the past.
These 180 case officers will have to decide whether the nature of previous convictions or other information, such as from employers, would be sufficient to bar someone from working with children or vulnerable adults.
Sir Roger said that about 10% of cases would then be monitored to assure the quality of such investigations.
As an example, he suggests there could be a discussion over whether a reformed former drugs offender should be considered sufficiently rehabilitated to give talks about drug abuse in schools.
This process would also have to tackle the problem of teachers facing false allegations, he said.
If there were doubts about the remit he emphasised that this was a scheme introduced by ministers and MPs - and the ISA was implementing these instructions.
He also suggested that it would not be over-bureaucratic - as people on the register would not be required to update details when they changed address or job.
Responding to the changes in the scheme, the ATL teachers' union leader, Mary Bousted, said these were "sensible recommendations".
"However, we still have major concerns about the scheme, particularly the duplication of running a CRB and ISA scheme alongside one another," said Dr Bousted.
"We are unhappy that there is still no right of appeal in person for anyone who is barred by the scheme - this seems to go against the laws of natural justice."