They are being trafficked and forced to work as prostitutes, domestic servants or enslaved in debt bondage and compelled to toil away in factories and farms, according to the study.
The Global Slavery Index for 2016 found that every corner of the globe is affected by slavery, but it is worst in Asia.
The highly secretive country of North Korea had the highest prevalence with 4.37 per cent of its population enslaved, followed by Uzbekistan at 3.97 per cent and Cambodia with 1.65 per cent.
India has the highest number of modern slaves with an estimated 18.35 million followed by China with 3.39 million and Pakistan with 2.13 million.
The report hailed the UK as having “led the world” in its anti-slavery strategy. The 2015 Modern Slavery Act toughened up laws and increased the sentence for the worst offenders to life imprisonment.
Andrew Forrest, the chairman and founder of the Walk Free Foundation, which compiled the report, urged world leaders to follow Britain’s example.
Speaking ahead of the report’s launch in London yesterday, he said: “One of the reasons why we chose to launch the Global Slavery Index 2016 in London was because of the leadership which Britain has made on the modern slavery issue.
“The Modern Slavery Act 2015 led the world and we are seeing this having a real impact in how companies and countries behave. We feel very strongly that if this leadership is adopted by the nine other major economies of the world then the world would be a much safer place.”
The report found that 45.8 million men, women and children are modern slaves – 10 million more than the last survey in 2014.
Mr Forrest maintained that the rise was down to better and more data, although he said he also believes the number of those enslaved is increasing.
He said: “It isn’t necessarily that fact that slavery has increased, we can’t prove that, what we can prove is that the metrics of visibility, the hard data, is better.
“Although my gut feeling is that it is actually increasing still and it will be a year or two before it turns around. But it is going to turn around, the way the world is waking up to it.”
The Home Office estimates that about 13,000 people are in modern slavery in Britain. Out of these people, the largest proportion is from Albania, followed by Nigeria and Vietnam, but many are British nationals, often teenage girls groomed and forced into sex work.
While the report singles Britain out for praise, it warned that conviction rates remain low and immigration rules tying migrant domestic workers to their employers leave them more vulnerable to exploitation.
Earlier this year, a Yorkshire bed company boss supplying firms including John Lewis and Next was jailed for employing slave labourers.
Mohammed Rafiq, from Batley, became the first company owner to be convicted over modern slavery offences. He sourced the Hungarian nationals at his bed-making factory, Kozee Sleep, in Dewsbury, making them work up to 16 hours a day for as little as £10 per week.
Fiona David of the Walk Free Foundation, an Australian-based NGO, said the refugee crisis sweeping through the Middle East and Europe has left people vulnerable to traffickers. But she said many entrapped in slavery in Britain are themselves British.