According to the National Crime Agency, criminal gangs successfully smuggle “thousands” of people into the UK undetected every year.
According to researchers, networks 'help' migrants pass through border controls through numerous visa and settlement schemes.
In an alarming assessment, the NCA said the threat from “organised immigration crime has increased”.
Most of them are likely to travel through the airport arrivals hall with false documents, rather than hiding in trucks or crossing the Channel.
The National Crime Agency outlined the range of risks facing Britain, saying “there has never been a more dangerous time to use drugs” due to the rise in cocaine production, the increasing availability of synthetic opioids and the increasing flow of cannabis into Britain.
The UK must brace itself for a widespread outbreak of synthetic opioids – similar to those plaguing cities in America – as demand for a stronger ‘high’ increases.
Highlighting how gangs are targeting Britain's borders to smuggle people and goods into the country, the National Crime Agency said: “Organised crime groups are helping migrants to fraudulently obtain permission to enter the country via 'leave to enter' or 'leave to remain' in the UK under various visa or settlement schemes. By definition, successful deceptions go unnoticed, but it is likely to affect thousands of people each year.
“Evidence suggests that organised immigration crime groups pose a persistent threat and it is highly likely that the threat from organised immigration crime will have increased as we head towards 2024.”
Graeme Biggar, Director General of the NCA, stressed that the UK faces a growing threat on several levels.
Mr Biggar said drugs were the biggest driver of organised crime in the UK and remained the “most important type of crime” the law enforcement agency had to tackle. He expressed concern about the “significant” number of deaths linked to the “incredibly potent” synthetic opioid nitazene in the past year.
Safety chiefs are growing concerned about the rising number of drug deaths in Britain, which are now “among the highest in Europe”.
And despite a decline in 'street crime', the 'scale and damage of serious and organised crime has increased'.
Nitazene has been used to potentiate heroin, the NCA believes. Since the “surge” began in June last year, there have been 284 confirmed deaths involving nitazene or its derivatives.
This number is likely to increase as investigations into other deaths continue.
Mr Biggar said: “That's a relatively small proportion of total drug deaths, but it is growing. It is significant.
“Nitazene can kill you the very first time you take it, and with nitazene you often don't even know you're taking it.
“It's heroin that's been adulterated. It's been put in a pill that you think is something else. And so anyone, a teenager, could take a drug thinking it's something else, and it's nitasene. It's incredibly strong, and you're going to die.”
In most cases of nitazene, the substance was “taken inadvertently with other drugs, such as heroin and/or benzodiazepines, with very small amounts potentially resulting in overdose and death”, according to a document setting out the NCA's national strategic review. It also said: “We need to prepare for the availability of these substances, both unannounced in enhanced mixtures and in response to user demand as a more powerful high.”
The NCA has admitted there has been an increase in the number of passengers arriving at UK airports with cocaine and cannabis in their luggage.
Rob Jones from the NCA added: “Over the years we have become very good at investigating sophisticated couriers who have fake compartments in suitcases, but what we are seeing at the moment is an increase in people checking in bags literally full of drugs.
“These have 30kg in a suitcase, without any form of concealment, cannabis wrapped in plastic and multiple couriers on the same flight.”
Mr Biggar said: “While overall crime rates have fallen over the past decade, the scale and harm of serious and organised crime has increased.
“As we stated in our last assessment, it is clear that serious and organised crime continues to cause more harm, to more people, more often, than any other threat to national security.
“No part of our society is immune to its consequences.
“We are working with social media companies to remove online ads placed by people smugglers to encourage people to make the dangerous journey across the Channel, and we have locked up people who thought they could hide on the dark web to facilitate child sexual abuse.
“And we are more determined than ever to tackle the organised criminals and gangs responsible for crossing the Channel in small boats. We have seized more than 400 boats and engines in the past year.”
The NCA said in its Strategic Threat Assessment that as many as 840,000 adults pose a risk to children.
Researchers said “the scale, complexity and severity of the threat of child sexual abuse is likely to increase.”
Rani Govender, Online Safety Policy Manager at the NSPCC, said: “The NCA’s online threats review paints a worrying picture of increasing risks, with new technology both enabling abuse and preventing the identification of victims and perpetrators.
“It is critical that platforms using end-to-end encryption play their part and ensure they have measures in place to protect victims and identify and disrupt abuse.
“Ofcom must hold tech services to account and strengthen their plans to tackle child sexual abuse. The government can also demonstrate its commitment to protecting children from harm, wherever it occurs, by reviewing the Online Safety Act.”