MODERN slavery offences in England and Wales have increased more than 50 per cent in one year, according to police records.

There were 5,144 modern slavery offences recorded by the police in the year ending March 2019, data published by the Office for National Statistics (ONS) shows.

This is a 51 per cent rise from the previous 12 months, when 3,412 offences were recorded.

MORE NEWS:

And 6,985 potential victims were referred through the UK National Referral Mechanism (NRM) in the year ending December 2018 - a rise of more than a third (36 per cent) in a year.

This coincided with a 68 per cent increase in calls and submissions to the Modern Slavery Helpline over the same time period.

Because of the hidden nature of modern slavery, it is difficult to produce an accurate measure of its prevalence and there is no one definitive data source.

The ONS said "many victims also do not self-identify, which means that quantifying the number of victims is challenging".

Previous estimates suggest there may be anywhere from 10,000 to 136,000 modern slavery victims in the UK.

The organisation analysed figures from the police, Crown Prosecution Service, Modern Slavery Helpline, UK National Referral Mechanism, the Salvation Army and others.

Helen Ross, from the ONS Centre for Crime and Justice, said: "This is the ONS's first attempt to bring data sources together on modern slavery to help us better understand both the nature of this terrible crime and the potential demand on support services.

"While there is no one source or method available which accurately quantifies the number of victims in the UK, evidence suggests there have been improvements in identification since the introduction of the modern slavery acts in 2015. Yet this is only part of the story, as many cases remain hidden and unreported."

Almost a quarter (23 per cent) of the potential victims referred through the NRM in the year ending December 2018 were UK nationals.

Of the 2,251 potential victims supported by the Salvation Army in England and Wales in the year ending June 2019, 48 per cent had experienced labour exploitation and 39 per cent had experienced sexual exploitation.

Sir Bernard Silverman, Professor of modern slavery statistics at the University of Nottingham, said: "Modern slavery takes many forms, usually but not always involving trafficking of people across and within countries.

"Victims may be coerced into prostitution or otherwise sexually abused; they may become forced labourers in both legitimate and illegal areas of the economy; they may be in domestic servitude or involved in drug dealing or other illegal activities; they may be enslaved or exploited in many other ways, even as horrendous as organ harvesting.

"If we are to fight slavery effectively, an evidence-based approach is crucial."