A new report has revealed the number of people around the world subject to trafficking and exploitation as modern-day slaves.

Modern slavery, described by UK prime minister Theresa May as “cruel exploitation”, encompasses both forced labour and forced marriage as well as human trafficking both within and between countries, debt bondage and the sale and exploitation of children.

The Global Slavery Index, a biennial survey of the international trade of people and goods that are reliant on the slave trade, reveals that 40 million people around the world are being held as modern-day slaves. The majority are in forced labour - 24.9 million - with 15.4 million held in forced marriage. And 70 per cent of all those living as slaves are women and girls.

The report says that the figures are likely to be an underestimate because of the lack of data from regions such as the Arab States and on practices such as the kidnap of children by armed groups and the number of people held for organ trafficking.