How does modern slavery happen in London?

NEW YORK, NY - SEPTEMBER 23: Jessica Penaranda of New York protests against labor trafficking and modern day slavery outside the United Nations on September 23, 2013 in New York City. The U.N. General Assembly convenes tomorrow, bringing politicians and business leaders from around the world to New York. (Photo by Andrew Burton/Getty Images)
NEW YORK, NY - SEPTEMBER 23: Jessica Penaranda of New York protests against labor trafficking and modern day slavery outside the United Nations on September 23, 2013 in New York City. The U.N. General Assembly convenes tomorrow, bringing politicians and business leaders from around the world to New York. (Photo by Andrew Burton/Getty Images)

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    How does modern slavery happen in London?

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CNN's Max Foster speaks with author Andrew Boff about how modern day slavery happens underneath our noses.