(CNN)The number of identified victims of modern slavery and human trafficking in London has risen more than tenfold in the space of five years, according to a new report which analyzes police data.
The UK has thousands of people in modern slavery -- and in London it's getting increasingly worse
Data from London's Metropolitan Police shows a 1,154% increase in the number of recognized victims of modern slavery -- from 187 referrals in 2013 to 2,346 in 2018.
More than 30% of the 5,143 people referred by the Home Office in 2017 for support were in London -- nearly three times higher than any other region or country in the UK, according to a letter from the London Assembly's police and crime committee.
In October, the Local Government Association said that the number of council referrals of suspected child victims of modern slavery in England had risen by 807% between 2014 and 2018.
London needs to have a "more coherent" strategy to tackle modern slavery and human trafficking, the London Assembly's police and crime committee said in a letter to the deputy mayor for policing and crime, Sophie Linden.
Unmesh Desai, chair of the committee, said in the letter: "The rise of modern slavery cases in London over the last five years shows that action is needed now."
The letter recommends a specific strategy is developed for the capital to improve its response to the problem.
It also recommends that the Home Office reforms the National Referral Mechanism (NRM), which is a process set up by the government to identify and support victims of trafficking.
Laura Durán, senior policy and research officer at Every Child Protected Against Trafficking, told CNN that despite a rising number of victims being identified, funding has not increased.
Durán said: "Austerity policies have weakened victim support and prevention work, leaving many destitute and vulnerable to further exploitation."
Patrick Ryan, chief executive of Hestia, a charity which supports victims of modern slavery in London, told CNN that one challenge was to address "failures in the training of frontline officers" -- which might put victims off going to the police.
The global slavery index for 2018 estimates there were 136,000 people in the UK living in modern slavery on any given day in 2016.
The assembly's letter comes just months after 39 Vietnamese people died in a lorry in Essex, England, in October.