Organised crime poses such a threat to the UK that an extra £3bn will be needed to fight it over the next three years, the National Crime Agency says.

Its head Lynne Owens says this includes more than doubling the NCA’s annual budget from £424m to nearly £1.1bn. In a speech, she warned the public will “feel the consequences” if the government does not find the cash.

The agency’s annual review of organised crime says there are more than 4,500 groups with 37,000 members in the UK. But it says the threat from these offenders is rapidly changing “in scale and complexity” – and it needs a vast increase in resources to keep up.

Ms Owens told BBC Radio 4’s Today show that the NCA is facing a “chronic and corrosive threat”. She said: “It’s a number of things, it’s globalisation, it’s the rapid use and expansion of technology, it’s the development of encryption and it’s the demand for services – it’s the supply of drugs, and we are a nation unfortunately, with a high demand for drugs. “It’s paedophiles using the dark web to target children in their bedrooms, those who dominate communities using fear and violence through the trade of drugs and firearms and illicit finance and cyber crime.”

When asked about reports indicating that the number of organised crime groups has fallen over the past year, Ms Owens said “that’s quite an old-fashioned way of looking at things.

“For example offenders operating on the dark web might only network through technology. So they won’t be part of a traditional organisation, but they are a network of like-minded individuals and that is why we get to a higher figure of offenders.”

At present the NCA spends £424m a year and has approximately 4,500 staff. By contrast, it estimates that 181,000 offenders can be ultimately linked to serious and organised crime, which has been moving into a far wider range of activity – from drug dealing through to people trafficking, cyber extortion and the trade in online sexual abuse imagery.

Ms Owens calculates that British investigators now need an extra £2.7bn over three years – to include an extra £650m annually for her agency. She says that extra cash would be less than the weekly estimated cost of organised crime to the UK. “Enhancing our capabilities is critical to our national security. If we don’t, the whole of UK law enforcement, and therefore the public, will feel the consequences. Some will say we cannot afford to provide more investment, but I say we cannot afford not to.”

Responding to the NCA’s call for more cash, security minister Ben Wallace acknowledged the scale of the threat – but did not immediately promise any more spending. “Our serious organised crime strategy, published in November 2018, set out how we will mobilise the full force of the state to target and disrupt serious and organised crime. “As criminals’ use of technology evolves so must our response. We continue to invest in the right capabilities and tools in law enforcement, across government and in partnership with the private sector.” The NCA’s sixth annual review of organised crime says groups have been fragmenting and capitalising on new technology not only to hide their identities but to increase their profits.

The rise of virtual or crypto currencies – which can be exceptionally difficult to track – is helping offenders launder their profits more efficiently without leaving a trail for investigators to pick up.

On cyber-crime specifically, the UK is fighting sustained attempts by Russian-speaking gangs to make money by targeting British computers – either through ransom attacks that lock up systems or through the theft of personal banking credentials.

One of the biggest threats has been the rise in sites in hidden parts of the internet where images of sexual abuse of children are traded. The NCA estimates that 144,000 of the people involved in these dark web sites are based in the UK – 5% of all known users. And it warns that Brexit will not only affect the ability of the NCA to work efficiently with its partners in the EU but could also lead to an increase in bribery and corruption as British companies enter into new markets around the world.