Tens of thousands of slaves could be living in the UK, a new report has claimed.

A study of modern-day slavery by the Walk Free Foundation says there could be two slaves for every 1,000 people in the UK - amounting to 136,000 victims across the country.

It also says British consumers could be unwittingly buying billions of pounds of goods made by people trapped in the slave trade in other countries.

The UK imports £14bn ($18bn) worth of goods each year which the foundation believes are at high risk of being made by slaves - including electronics like laptops and mobile phones, clothes, cocoa, sugarcane and even fish.

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Cocoa is one industry with a particularly high level of risk of forced labour.

The report focused on analysing G20 countries and their levels of imports of at-risk products, finding G20 countries together import about £271bn ($354bn) annually of products which could have been made by slaves.

Only seven of the G20 countries, including the UK, have enacted laws which attempt to minimise the impact of modern slavery on supply chains.

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The report notes: "The UK Modern Slavery Act (MSA) has been described as a 'game changer' for tackling modern slavery and requiring transparency on modern slavery in supply chains."

The MSA requires all companies with a turnover of £36m or more which provide goods or services in the UK to produce an annual report to explain how they are tackling slavery in their supply chains.

Kevin Hyland, the UK's independent anti-slavery commissioner, said the law had "undoubtedly" served to raise awareness of slavery and had given year-on-year increases in the number of slaves being identified.

He added: "It is unacceptable that modern slavery continues to exist in a climate of low risk criminality and high profit reward making it the crime of choice for criminals who for too long have operated with impunity in the UK and beyond."

In an essay published alongside the report, Fiona David, the executive director of global research for the Walk Free Foundation, said: "The 2018 Global Slavery Index confirms that governments are taking more of the steps we ask of them to respond to modern slavery - strengthening laws, training police, providing services and shelters to victims, and engaging with businesses on supply chain transparency."

But she continued to say the laws will have little impact without implementation and enforcement, while police training is worthless if a judge can be bought.

Ms David also criticised the US for withdrawing on discussions in the UN on refugees and migration, saying it was "unthinkable" that so many leaders had agreed on so much, except for the safe travel of people around the world.

Top 10 countries with highest level of modern-day slavery

North Korea Eritrea Burundi Central American Republic Afghanistan Mauritania South Sudan Pakistan Cambodia Iran

Top 10 countries with highest response to modern-day slavery