High levels of organised crime across the country are linked to immigrants and asylum-seekers, according to one of England's most senior police officers.
There is no accurate record of asylum seekers living in the UK
People-smuggling, prostitution and drug dealing are among the crimes linked to immigration by Chris Fox, president of the Association of Chief Police Officers (ACPO).
Immigration and asylum are also being used as a cover by criminals to enter the country, he told BBC One's Breakfast.
But, he said the vast majority of immigrants were not involved in crime.
Every force in England has investigations abroad into crime committed by people who had entered the country both illegally and legally, he added.
His comments came on the first day of the Acpo annual conference in Birmingham.
Earlier he warned a "tidal wave" of mass immigration had brought a "new wave of crimes", in an interview with the Observer newspaper.
"Mass migration has brought with it a whole new range and a whole new type of crime, from the Nigerian fraudster, to the eastern European who deals in drugs and prostitution to the Jamaican concentration on drug dealing," he said.
"My personal view is that this is a small island.
"We have some very, very intensely-populated areas and I think we have to be careful just how we let the mix develop.
"It's healthy that we've got lots of different people, but if you go into some of the cities, looking at the north, Bradford simmers, Blackburn simmers."
The far-right British National Party won eight council seats in Burnley earlier this month, and Bradford and Oldham suffered race riots last summer.
Mr Fox said it did not take much to disturb that balance
"We've got to be very careful to make sure that we're not overwhelming our current infrastructure," he said.
A report by the influential House of Commons Home Affairs Select Committee published earlier this month said the large number of asylum-seekers was threatening "social unrest" and had to be curbed.
Meanwhile the figures for numbers seeking asylum in the first quarter of this year are due to be released on Thursday.