The rise includes people lured to the country after meeting people via online dating or job recruitment siteschina virtual office.
Romania remains the most likely country of origin for victims, followed by Poland and the UK.
The NCA says trafficking does not have to involve crossing international borders.
Investigators say the rise is partly down to better reporting, including an increase in the number of children feared to be victims of sexual exploitation gangs.
False benefit claims
Overall, the agency says there has been a 22% jump in the number of identified suspected victims of trafficking between 2012 and 2013.
The 2,744 suspected victims, thought to be the tip of the iceberg, include 602 childrenSim .
The NCA says there has been a surge in reports of sexually exploited children - from 38 to 128 - in the wake of high-profile abuses cases in Rotherham and elsewhere.
Investigators also found cases of adults forced into prostitution, labour exploitation, domestic servitude, or compelled to commit crimes such as making false benefit claimshair loss treatment .
周向榮She said that the migrants were costing too much and making life unpleasant.
Many believe the UK will be a more welcoming place if they can get there.
In 2002 the French government closed the main Red Cross centre at Sangatte near Calais, but unsanitary illegal camps have constantly sprung up in its place since then.
Migrants queue for food in Calais, France (5 August 2014) Calais has been a magnet for migrants hoping to get to the UK for much of the last decade
Members of an NGO distribute food to migrants in Calais (5 August 2014) It is is estimated that there are about 1,300 illegal migrants in Calais, many of whom rely on food handouts
In recent months French police have tried to break up the camps, but the migrants say they have nowhere else to go. They can be seen sheltering under plastic bags and sheets, and many depend on charities for food.康泰
"I could take the decision to block the port. I could bring pressure to bear," Ms Bouchart told journalists in Paris after discussing the problem with Interior Minister Bernard Cazeneuve.
"It would be illegal," she accepted, "but today I want to make a strong gesture towards the British."
The mayor complained that British immigration policy made the UK be seen as "an Eldorado" by immigrants.
She criticised Britain for demanding security is boosted at Calais on the one hand without sufficiently financing the 10m euros ($13m; £7.8m) improvement project on the other.
The mayor said that while she had not discussed her port blockade idea with Mr Cazeneuve but she urged him to open "strong negotiations with the British".
The minister - who was in the UK last week - has appealed to Britain to help finance security at the port, ministerial sources quoted by the AFP news agency said.周向榮