Crimefighters have warned that live online child abuse and the trade in drugs and guns will be growing threats to the UK in the next three years.
The first nationwide assessment by the National Crime Agency (NCA) found that paedophiles will increasingly use the "hidden web" - internet content that is not accessed by popular search engines - to access images of child abuse.
More heroin will be imported from Afghanistan, where the opium poppy crop boomed particularly in Helmand province as British troops withdrew, and more amphetamines and so-called "legal highs" will be made in the UK.
Criminals will also increasingly exploit legitimate channels for bringing guns into the country to get their hands on weapons, the assessment said, and could be used by terrorists.
The report said: "We assess that criminal exploitation of the legitimate supply of firearms to the UK marketplace will increase. There is also a concern that weapons, whether from illegal or legitimate sources, might find their way into the hands of extremists."
The NCA expects more attacks to be staged on UK computer networks with viruses and distributed denial of service attacks, where websites are deliberately overwhelmed, particularly on government pages.
The report said: " If there is a single cross-cutting issue that has changed the landscape for serious and organised crime and our response against it, it is the growth in scale and speed of internet communication technologies.
"The online streaming of real-time child sexual exploitation and abuse is a growing threat. Cyber techniques have proliferated and are used ever more extensively by wider serious and organised crime groups to commit 'traditional' crimes.
"As more government services go online, including tax collection, there is an increasing risk of online attacks and fraud against the public sector.
"The pace of development of deployable criminal tools is such that we anticipate an increase in the targeted compromise of UK networked systems, more ransomware attacks and distributed denial of service (DDOS) attacks against business-critical systems."
The NCA's National Strategic Assessment also found that millions of pounds gained from bribery and corruption overseas and billions in criminal proceeds are laundered through the UK.
NCA director-general Keith Bristow said: " This assessment, which is the first one published by the NCA, is the most detailed and broad-ranging crime threat analysis ever produced by law enforcement.
"The assessment, and the response to it, is owned by the whole of law enforcement, including police forces and other national agencies, as well as Whitehall departments, local government, industry partners and the third sector.
"It helps us maximise our collective impact in order to cut serious and organised crime."
The head of professional practice at the College of Policing, Giles Herdale, said 6,000 detectives will be trained this year specifically in tackling online crime.
He added: "The National Crime Agency's report shows that as the internet has changed how many people communicate, organise and trade, it has also brought criminals new opportunities.
"The speed at which these changes have taken place has challenged the police service to ensure that our officers and staff are equipped with the right skills to tackle crime.
"The College of Policing is taking steps so that knowledge around cybercrime is seen not as a specialism in policing but as a core part of any investigator's knowledge."