The British Home Office has estimated that there are around 13,000 victims of slavery in the UK.
The victims include women forced into prostitution and children who are exploited as well as people made to work in fields, factories and on fishing boats.
In what is said to be the first scientific estimate of the scale of modern slavery in the UK, the Home Office said the number of victims last year was between 10,000 and 13,000.
Data from the National Crime Agency's Human Trafficking Centre had previously put the number of slavery victims in 2013 at 2,744.
Home Secretary Theresa May said the scale of abuse was "shocking".
"The first step to eradicating the scourge of modern slavery is acknowledging and confronting its existence," she said.
"The estimated scale of the problem in modern Britain is shocking and these new figures starkly reinforce the case for urgent action."
Director of Anti Slavery International Aidan McQuade warned that policing measures alone would not resolve the issue.
He said that protection of victims needed to be placed on a statutory footing in order to reassure those who came forward that they would not themselves be treated as criminals or face deportation.
"It is something that the government seems loath to consider because it is confusing this debate with the migration one and that is a poisonous conflict at the moment," he told BBC Radio 4's Today.
"For many of the victims of trafficking, the police aren't somebody that they would necessarily assume are going to be their friends because of their backgrounds and where they are coming from."