The National Crime Agency (NCA) said UK-based companies that increase trade outside the EU are more likely to come into contact with corrupt markets, particularly in the developing world.
Criminals will have more opportunities to carry out “trade-based money laundering” and there will be an increased chance that British businesses are “drawn into corrupt practices”, the agency said.
Publishing its annual assessment of serious and organised crime, the NCA said that while the result of the EU referendum has had little impact on crime in the UK, Brexit would be a “key driver of uncertainty in the next five years”.
“Criminals are not constrained by geographical or jurisdictional boundaries and are inherently opportunistic,” the NCA said.
“We expect that many will strive to take advantage of the opportunities that Brexit might present.”
It added: “As the UK moves towards exiting the EU in March 2019, UK-based businesses may look to increase the amount of trade they have with non-EU countries.
“We judge this will increase the likelihood that UK businesses will come into contact with corrupt markets, particularly in the developing world, raising the risk they will be drawn into corrupt practices.”
The NCA warned that criminals may try to take advantage of a redesigned customs system after Brexit, or gaps in intelligence-sharing between countries.
Its annual review summarised the threat of crime in the UK including child sexual exploitation and abuse, modern slavery and human trafficking, organised immigration crime, cyber crime, money laundering, drugs and guns.
In detailed findings, the wide-ranging assessment said:
:: There were 4,629 organised crime groups in the UK at the end of last year, according to NCA analysis
:: The UK’s 3,000-plus airstrips present opportunities for criminals to exploit the border to facilitate the illegal entry of migrants
:: Encrypted communication services are eroding the ability of law enforcement to detect dangerous offenders
:: The closure of migrant camps at Calais and Dunkirk has reduced the scope for “opportunistic” attempts to enter the UK from France, but Belgium has become a location of “greater focus” for people smuggling gangs
:: There has been an upward trend in criminal firearms discharges, with a surge in the number of parcels arriving into the UK being exploited by gangs “concealing illicit goods amongst legitimate traffic”
:: The UK is a “prime destination” for corrupt foreign “politically exposed persons” to launder the proceeds of corruption
:: Mobile phones in prisons give offenders involved in serious organised crime the means to play a “full role” in major criminal enterprises “virtually unaffected by physical confinement”.
:: The scale of modern slavery and human trafficking in the UK is continually and gradually increasing.