How many people in the UK are victims of modern slavery? At present, we don’t actually know. There is no consensus on the answer to this question, despite the wide interest in finding it, and the tools and data to do so.

Over a decade ago, before the passage of the UK Modern Slavery Act 2015, data analysts estimated that there were between 10,000 and 13,000 victims of modern slavery in the UK. Since then, there have been four further estimates between 2014 and 2023, ranging from 8,300 to 136,000.

Why such a huge range? Estimates use different indicators and definitions of modern slavery, as well as different estimation methods.

Several parliamentary inquiries have now been conducted focusing on how the UK can strengthen its response to modern slavery. Part of an effective response is understanding the nature and extent of the issue. And this understanding relies on better methods to produce statistically robust estimates of the scale of the problem.

The UK Independent Anti-Slavery Commissioner asked our team of researchers at the University of Nottingham’s Rights Lab to carry out a

© The Conversation