A new report, the first scientific estimate of the scale of modern slavery in the UK, has shown that the number is four times what was previously thought.
Victim levels are estimated to be between 10,000 and 13,000 including women forced into prostitution, domestic staff and workers in fields, factories and fishing boats.
Home Secretary Theresa May said the scale of abuse was "shocking".
She added: "The first step to eradicating the scourge of modern slavery is acknowledging and confronting its existence. The estimated scale of the problem in modern Britain is shocking and these new figures starkly reinforce the case for urgent action.
"That is why I have introduced a Modern Slavery Bill, the first of its kind in Europe. But I have always been clear that legislation is only part of the answer.
"The law must be rigorously enforced and we need wide-ranging activity. This Strategy sets out the Government's approach which puts victims at the heart of everything we do.
"Everyone must play their part if we are to consign slavery to history where it belongs."
Home Office Chief Scientific Adviser Professor Silverman said: "Modern slavery is very often deeply hidden and so it is a great challenge to assess its scale. The data collected is inevitably incomplete and, in addition, has to be very carefully handled because of its sensitivity.
"I very much hope that we will be able to build on these results and this approach to help tackle this issue, not just in this country but worldwide."
Speaking last year about the Modern Slavery Bill the Archbishop of Canterbury Justin Welby said: "The Home Office has been a leader in the field of tackling modern slavery, and the determination of their approach is notable.
"I also hope that the Government will bring forward a Bill as quickly as possible to ensure there is sufficient time to get it through Parliament. I, along with many others, will be closely following the Bill's passage, and I look forward to contributing to its scrutiny in the House of Lords.
"This pioneering bill sets a high standard for Governments around the world, who will be watching to see how our Government handles the issue of modern slavery.
"It is vital that it seizes this opportunity to continue to set a gold standard that others can follow.
"People of faith are determined to contribute to combating modern slavery and human trafficking. It is vital that we all work together to tackle this modern day evil so that all people live in freedom and dignity."