Iconic British landmarks including 10 Downing Street and Marble Arch have been lit up red to mark anti-slavery day in the UK.
The Home Office, Cabinet Office and Foreign Office also turned red on Thursday evening as the Government displayed its backing for new measures to tackle modern slavery.
Anti-slavery day aims to raise awareness of child trafficking in the UK, with more than 2,000 suspected victims reported to authorities in 2017.
Other buildings including Edinburgh Castle, Croydon Town Hall, Marks and Spencer at Oxford Circus and the Co-op headquarters in Manchester were also lit up red.
To mark anti-slavery day, the Government announced it is stepping up measures to tackle modern slavery by warning thousands of businesses they face action if they fail to meet legal obligations.
The Home Office is writing to 17,000 chief executives telling them to "open up" about modern slavery in companies which supply them with goods and services.
Businesses with a turnover of more than £36 million have to publish annual statements setting out what they are doing to stop modern slavery, but fewer than two in three have complied and some are said to be of poor quality.
Minister for Crime, Safeguarding and Vulnerability Victoria Atkins said: "It is horrible to think some of the goods and services we buy could have been produced by someone forced into modern slavery. This is abhorrent and as global leaders in the fight against modern slavery, we will not tolerate it.
"Some businesses are already leading the way in taking action by being open and transparent about what they are doing to identify, tackle and prevent forced labour in their supply chains, but too many are still failing to meet their basic legal obligations.
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"That's why the Home Office is sending letters to businesses today with a clear message that continued non-compliance will not be tolerated."
The Environment Agency said it had trained over 100 officers to recognise exploitative work practices.
Marie Fallon of the agency said: "Whilst the majority of the waste businesses we regulate are well run, there are a concerning number of operators who delve into criminal practices which harm the environment, local communities and their own workforce."
