Some convicted paedophiles are still committing sex abuse abroad despite the tightening of rules aimed at stopping them, campaigners say.
Gary Glitter was convicted of sex offences in Vietnam this year
People on the UK's Sex Offenders Register can travel abroad for up to three days without notifying police - before the time allowed was eight days.
But Ecpat UK says the "loophole" means offenders can still reach vulnerable children in central and eastern Europe.
The Home Office said it was looking at possible further restrictions.
The number of days a convicted sex offender can stay overseas before they need to notify the police was reduced under the 2003 Sexual Offences Act for England and Wales.
This year, the most prominent Briton to be convicted of abusing children abroad, singer Gary Glitter, was jailed in Vietnam.
The first conviction in a UK court for sex offences committed abroad also took place when a man who abused children in Africa was jailed.
Ecpat, however, cites cases of child sex abuse involving British nationals in the Czech Republic, Romania, Bulgaria, Spain and France.
"One of the misconceptions legislators had at the time was that [child abuse] only happened in far-flung places like Thailand and the Philippines," said the campaign's director Christine Beddoe.
"It is an international problem that can affect every country, even those closest to home."
Ecpat said progress had been made over the last 10 years with new laws and the launch of the Child Exploitation and Online Protection Centre.
But it called for a "comprehensive, co-ordinated partnership" involving the likes of the police, the Home Office, embassies and the travel industry.
It said a growing numbers of Britons were abusing children in orphanages and other institutions abroad.
Some abusers do not come to the attention of the authorities because they are not convicted sex offenders, Ecpat added.
It renewed calls for the law to be changed so that UK prosecutions of an overseas act no longer required the abuse to be illegal in the country where the offence was committed.
The Home Office said safeguarding children from the risk of sexual harm was a "key priority".
"We introduced the Sexual Offences Act 2003 which contains a new range of sexual offences specifically designed to give children the maximum protection that the law can offer," a spokesman said.
"We continue to monitor the effectiveness of the legislation.
"We reviewed our policy and practices with regard to travelling sex offenders earlier in the summer and we are in the process of deciding what further steps are necessary, if any, to ensure that we are doing all we can to keep children safe from sexual abuse wherever they may be."