Writing in The Sunday Telegraph, the prime minister said it was "the great human rights issue of our time".

A new cabinet taskforce will tackle the "sickening and inhuman crimes... lurking in the shadows of our country".

More than £33m from the aid budget will be used to fund initiatives in nations from where people are trafficked.

The most recent Home Office estimates suggest there are between 10,000 and 13,000 victims of modern slavery in the UK, with 45 million estimated victims across the world.

'Locked up, abused'

Victims are said to include women forced into prostitution, "imprisoned" domestic staff and workers in fields, factories and fishing boats.

Mrs May said: "From nail bars and car washes to sheds and rundown caravans, people are enduring experiences that are simply horrifying in their inhumanity.

"Vulnerable people who have travelled long distances, believing they were heading for legitimate jobs, are finding they have been duped, forced into hard labour, and then locked up and abused.

"Innocent individuals are being tricked into prostitution, often by people they thought they could trust. Children are being made to pick-pocket on the streets and steal from cash machines." Mrs May said a review to mark the first anniversary of the Modern Slavery Act, which she drew up as home secretary, found there had been 289 modern slavery offences prosecuted in 2015 - and a 40% rise in the number of victims identified.

But barrister Caroline Haughey also found police and criminal justice agencies lack consistency in dealing with the issue.

Mrs May said the first ever government taskforce on modern slavery will see ministers "get a real grip of this issue right across Whitehall and co-ordinate and drive further progress in the battle against this cruel exploitation". Her Majesty's Inspectorate of Constabulary will also be asked to carry out an investigation to make sure that all police forces in England and Wales "treat this crime with the priority it deserves".

"[The government] must work collaboratively with law enforcement agencies across the world, to track and stop these pernicious gangs who operate across borders and jurisdictions," Mrs May said.

She added: "These crimes must be stopped and the victims of modern slavery must go free...

"Just as it was Britain that took an historic stand to ban slavery two centuries ago, so Britain will once again lead the way in defeating modern slavery and preserving the freedoms and values that have defined our country for generations."