London is often the first stop for UK victims of trafficking
Proposals by the Metropolitan Police to disband its specialist human trafficking team have been attacked by several leading charities.
The charities, including the NSPCC and Amnesty International, say the move would be seriously detrimental to the fight against trafficking.
They have written to Met Commissioner Sir Paul Stephenson appealing for the unit not to be disbanded.
The Met said the team, set up in 2007, had direct funding for three years.
A final decision on whether the move will go ahead is expected within weeks.
The BBC's June Kelly says in the team's short history, it has already been threatened with closure once before, because of funding problems, and later given a reprieve.
Now once again there is a proposal to disband a team which has been described as an international example of good practice, our correspondent says.
If the trafficking team is disbanded, the proposal is for its work to be given to other Met officers.
The charities, which also include End Child Prostitution and Trafficking and the Poppy Project, which helps victims of trafficking, have banded together to protest.
They stress that with victims traded for different reasons - including sex, forced labour, and domestic servitude - specialist policing is needed.
In their letter, they say: "Human trafficking is a complex, sensitive issue.
"Given the continually evolving nature of the crime, it has taken the Human Trafficking Team and Non-Governmental Organisations working in the field a number of years to develop their expertise in the area.
"Policing trafficking for forced labour, domestic servitude and all other forms of exploitation requires specialist knowledge and understanding of trafficking, dedicated resources and commitment."
The charities also warn that when London plays host to the 2012 Olympics it could become even more of a magnet for the traffickers because experience shows that where large number of people gather there is an increased demand for sexual services.
A Met Police spokesman said it had been conducting a review about its response to "all organised immigration crime and trafficking".
"This has yet to be ratified but proposes clubs and vice [team] have enhanced resources and take over trafficking for sexual exploitation investigations."
Aidan McQuade, director of Anti-Slavery International, said getting rid of the team, "even if there are serious financial pressures", was "very dangerous".
"Clubs and vice have experience of trafficking for sexual exploitation but their remit does not cover trafficking for forced labour or domestic servitude," he said.
On the funding issue, the Home Office said there was a "clear understanding" with the Met "that any future funding as of 1 April 2010 would be met from its central budget".
A spokeswoman added that the Home Office provides funding to the Serious Organised Crime agency, which investigates human trafficking, and the UK Human Trafficking Centre, a police-led multi-agency centre which co-ordinates intelligence and operations.
London is often the first stop in the UK for victims. Human trafficking has been described as the third largest international crime, following illegal drugs and arms trafficking.
The nature of the crime means that the cases which are detected are the tip of the iceberg, according to one senior Met officer.
Giving evidence to the Home Affairs select committee in 2008, Commander Alan Gibson said: "I would not like to say how much of its is above water."
Commander Gibson said that in the previous two years the Met had dealt with 211 cases.