Labor experts in Britian urged the country's top 100 companies to be more transparent and lead by example. The average combined score of the 100 companies - 47 per cent - shows they are generally failing to take meaningful anti-slavery action and spur better practices in the private sector. Major retailer Marks & Spencer topped a list recently ranking Britain's biggest businesses on their efforts to tackle modern slavery.

Supermarket Tesco and British American Tobacco ranked second and third on the first Global Governance FTSE 100 League Table, which judged firms based on their compliance with Britain's landmark anti-slavery law, and overall human rights practices.

Under Britain's 2015 Modern Slavery Act, companies with a turnover of more than $47.5 million must produce an annual statement outlining the actions they have taken to identify and stop forced labour in their supply chains. Big brands in Britain and beyond are facing growing pressure from regulators and consumers alike to ensure that their global operations and products are not tainted by modern-day slavery.

While most companies on index were found to be largely compliant with the requirements of the law, only one in four of the companies were fully in line, the research found.