LONDON - Scotland Yard on Friday pledged to use modern slavery laws to crack down on gangs using children to run drugs from London to towns and cities around Britain.

British police are also working to shut down phone lines fuelling a trade estimated to be worth more than 500 million pounds (some $712.62 million) a year.

The warning to gangs came as two criminals faced jail on Friday after being convicted under modern slavery legislation in a landmark case.

Mahad Yusuf, 20, and Fesal Mahamud, 19, both from London, were due to be sentenced after pleading guilty to trafficking a young person for the purposes of exploitation under the Modern Slavery Act and conspiracy to supply Class A drugs.

They lured a vulnerable 19-year-old from London to Swansea and forced her to sell drugs, threatening her with violence if she tried to escape.

The pledge came just days after British Home Secretary Amber Rudd announced to earmark nine million pounds, or $12.82 million, for crackdown on paedophiles, organized gangs and other criminals who exploit the "dark web".

Rudd said that the nine-million-plus-pound funding was being provided to "enhance the UK's specialist law enforcement response."