Experts have warned that slavery is more profitable than ever with traders making 30 times more than in the 18th and 19th century.

Human rights researcher Siddharth Kara calculated that nowadays each victim makes an average of £3,030 a year for those who exploit them - with some making more than 10 times that figure.

Meanwhile sex trafficking makes up half of the profits of the illegal industry despite those victims only accounting for 5% of modern slaves. It can bring in profits of more than £27,000 per person.

Mr Kara told The guardian human life has become more expendable than ever.

'Slaves can be acquired, exploited and discarded in relatively short periods and still provide immense profits for their exploiters.

He added: 'Unless slavery is perceived as a high-cost and high-risk form of labour exploitation, this reality will not change.'

Kara's calculations were based on data from 51 countries recorded over a 15-year period as well as thousands of victims of slavery.

According to experts the scale of slavery has dramatically increased - with approximately 21 million people being exploited worldwide compared to the 13 million people who were sold as slaves between the 15th and 19th century. They were identified by police, charities and welfare experts as potential victims of so-called modern slavery, which includes human trafficking and forced labour.

But the figure could merely be the 'tip of the iceberg', with many more unreported cases, the study by the Children's Commissioner for England warns.

Anne Longfield has urged politicians to stamp out the 'horrendous exploitation' of youngsters by adults.

She said slavery was just one of several serious issues that forced millions of children across the country to live 'vulnerable or high-risk lives'.

Her report cites the latest figures from the Government's national referral mechanism (NRM), the official framework for identifying and helping victims of slavery and trafficking. Some 1,204 children aged up to 17 were referred to the NRM last year for suspected domestic servitude, labour or sexual exploitation in England – an increase of a third, from 901 in 2015.

British nationals were the biggest group at 247, with 209 of them feared to have been caught up in sexual exploitation.

They were followed by 223 Albanian youngsters, of whom 150 were referred for potential labour exploitation. The third highest source of referrals were 200 Vietnamese children, with 101 of them feared trapped in forced labour.

Nigerian children also made up 40 of the NRM referrals in 2016, with 18 of these for suspected domestic servitude.

However, the report says there are many 'invisible children' who may be 'particularly vulnerable' due to gaps in identification.

These youngsters may 'have been victims of modern slavery but not reported to the national referral mechanism'.