There could be up to 10,000 people working in slave-like conditions in Leicester's textile factories, a Leicestershire MP has said.
Andrew Bridgen has said there is a "conspiracy of silence" that has allowed factories in the city to continue to exploit workers over many years.
He told Sky News: "You've got a systemic failure of all the protections in Leicester that would prevent this from happening.
"I've estimated it's around 10,000 individuals who are effectively in modern slavery providing garments for internet retailers."
Justice Secretary Robert Buckland said it will take a "long time" to tackle the abuse of modern slavery which exists in "every town and city" in the UK.
Mr Buckland told Sky News: "A light has now been shone on an appalling litany of abuse and I'm glad to hear that the National Crime Agency (NCA) is now conducting an investigation, its got a lot of power to bring in various agencies to start the work of an investigation into this.
"Modern-day slavery is all around us, its in every town and city in Britain and indeed in our rural areas as well, it takes many forms.
"This type of exploitation, people being paid well below under the minimum wage, having to work in unacceptable conditions, that sort of abuse has to be stamped out, it has to be examined, we have to follow the evidence and prosecute wherever possible."
He added: "What has happened with modern slavery is that we've legislated on it, we've improved the response of the agencies and the authorities to it, but now its up to all of us in our communities to identify it, call it out and to do everything we can to stamp it out.
"This is not a job that's going to take weeks, it's going to take a long time but I welcome the investigation."
City in lockdown
Leicester city mayor Sir Peter Soulsby told BBC Breakfast that, having "finally" been provided with "useful data", they know that around 10 per cent of the city has recorded a higher transmission of the virus.
He said: "If we had known that weeks ago we could've actually dealt with it at that time and prevented this lockdown."
Sir Peter Soulsby said Leicester needed a more detailed breakdown of testing data in order to identify where the virus is being passed on.
The mayor told BBC Breakfast: "Even now we're getting it (the data), it doesn't have some of the vital stuff that we need, particularly in a city like Leicester.
"We need to know the ethnicity of the people who are being tested, we need to know where they are working. There's been all this talk about perhaps it's passed on in factories, but we have no way of knowing that."
Asked if he hoped the lockdown restrictions would be lifted soon, he said: "I very much hope so, yes."
But he added: "It was clear from discussions we were having last week with them (the Department of Health) that they haven't yet got a clue of how on earth they're going to measure what constitutes success in this.
"I mean even the data we're getting now is the best part of two weeks' out of date, and we need to be knowing, on a day-by-day basis street-by-street basis, what that data is telling us and then we can tell whether or not, in those particular neighbourhoods, we're actually combating the virus effectively."