Tighter controls on registered sex offenders travelling abroad could stop cases like Gary Glitter's happening again, children's charities say.
World Vision UK said existing laws allowing paedophiles to be banned from going abroad must be "used more".
Other charities have called for UK police to look at bringing charges against Glitter, 61, should he return.
The ex-UK rock star, real name Paul Gadd, was jailed for three years for molesting two young girls in Vietnam.
A Vietnamese court found him guilty on Friday of abusing the girls, aged 11 and 12, at his home in the resort town of Vung Tau, southern Vietnam.
After the verdict, World Vision called for more Foreign Travel Orders - which allow for paedophiles to be banned from places where they could abuse children - to be used.
The first of the orders, introduced in 2004, was made in January 2005, but the Home Office says it has no figures on the amount used.
On his release from prison, Glitter will be deported but the Foreign Office says it will be up to Vietnam to decide if that will be back to the UK or to a different country.
Christine Beddoe, of End Child Prostitution, Pornography and Trafficking (Ecpat), urged UK police to use British sex tourism laws to bring charges against Glitter if he returns.
"We would like to see a further investigation by the British authorities to see if it would be possible to bring a prosecution against him here," she said.
In addition to his prison sentence, Glitter has been ordered to pay 5m Vietnamese dong (£180/$315) to his victims' families.
During the two-day trial, most of which was held behind closed doors, he was said to have committed a series of "lewd" acts while the girls were at his beach house in Vung Tau.
Sentencing Glitter, Judge Hoang Thanh Tung said: "His lewd acts have compromised the dignity of the Vietnamese people, law and common sense, and therefore it is necessary to punish him."
The judge later told reporters he believed Glitter understood he had "a sickness".
After he was sentenced, Glitter suggested some British newspapers were part of a conspiracy against him.
"I haven't done anything - I am innocent. It is a conspiracy by you know who," he told gathered journalists.
As he was led away from the courthouse and into a prison van, Glitter, sporting a white goatee beard, held a clenched fist in the air.
The ex-rock star shot to stardom in the UK in the 1970s with hits such as Rock and Roll (Part 2) and Leader of the Gang - a No 1 single in the UK in 1973.
Known for his flamboyant stage persona and extrovert costumes, he continued touring for most of the 1980s and 1990s.
Glitter may be considered for release after serving a third of his jail term, which includes the four months he has been held in custody since his arrest.
His lawyer said his client had not yet decided whether to appeal against the decision.
Glitter as he appeared during his music career
The British embassy said in a statement: "Both the UK and the Vietnamese governments take the issue of child-sex tourism extremely seriously.
He had been in custody since 19 November when he was arrested in Ho Chi Minh City as he was about to board a flight out of Vietnam.
In December, Glitter's lawyer made compensatory payments to the families of the girls, who later appealed to the courts for clemency for Glitter.
He evaded more serious charges of child rape, which carry a maximum penalty of death by firing squad.
Glitter was convicted of possessing child pornography in Britain in 1999 and served half of a four-month jail sentence.
He later went to Cambodia, which permanently expelled him in December 2002 over suspected sex offences.