One in five convicted or suspected child sex offenders who travel abroad take jobs which give them access to youngsters, figures have shown.
They could have been banned from working with children in the UK but work freely abroad, as many schools and organisations overseas have no access to criminal record checks.
A new police system for UK nationals who are working or volunteering abroad will help identify those who have previous convictions which mean they should be banned from working with children, the Child Exploitation and Online Protection (Ceop) agency said.
The international child protection certificate (ICPC) will be "a worldwide safeguard" for employers and voluntary organisations, the agency's chief executive Peter Davies said.
Fourteen of the 75 travelling UK sex offenders investigated by Ceop in 2011 were associated with roles that involved access to children, figures released by the agency showed.
Some 1,235 such investigations have been carried out since 2006 with between 7% and 19% of these each year involving offenders who had access to children abroad.
"There is clear evidence to suggest that serious sex offenders who are known to authorities in the UK will often seek out opportunities to work or volunteer abroad," Mr Davies said.
"In many instances this will be through teaching roles but could equally be through other occupations such as charity worker, orphanage worker or as a children's home worker."
The new system comes after cases such as that of child sex offender Andrew Eden, who fled to Mexico and taught English in schools after being released from prison in the UK.
Eden, previously of Littleborough, Rochdale, was jailed for four years in 2001 when he was convicted of molesting a seven-year-old girl and was put on licence for an additional three years. But when he was released from custody in 2003 he failed to notify the authorities of his whereabouts and faced being recalled to jail, but fled to Mexico instead where he worked in schools.