Tony Blair launched Britain's version of the FBI today with a promise to make life hell for the gangsters, drug barons and people-traffickers who, he said, cost the country more than £20 billion a year.

Launching the Serious Organised Crime Agency (Soca) at Downing Street, the Prime Minister said the problem of organised crime was "greater than ever before".

He was backed by Charles Clarke, the Home Secretary, who said: "I am today sending the organised criminal underworld a clear message: be afraid."

The agency, incorporating the old National Crime Squads and National Criminal Intelligence Service, will have 4,000 staff, including specialists from MI5 and MI6, and 120 officers based overseas. Its top priorities will be tackling the illegal drugs trade and human trafficking.

"There is a class of highly entrepreneurial international criminals who have turned their ingenuity to malign effect," Mr Blair said. "We are not dealing with shambling amateurs. It is a global business, its captains are practical and we have to be equally tough, intelligent, broad-ranging and rigorous in return."

Mr Blair said that the social and economic costs of the class A drugs trade alone is £13 billion a year. Immigration crime costs a further £1 billion. Mr Blair said that it was imperative that the Government acted to end the damage organised criminal networks were doing to the fabric of communities.

The new agency will also tackle fraud, identity theft and online crime, which is estimated to cost the UK economy around £2 billion a year.

Mr Blair said Britain could no longer fight 21st century criminals with early 20th century methods. "The old methods of the way we try to police and investigate and use intelligence are not going to work when confronted with highly efficient criminal gangs," he said.

Apart from succeeding the existing national agencies, Soca will also incorporate functions of the immigration and customs agencies, meaning that its officers will be the first in the country to combine the powers of police, immigration and customs officers to ensure the agency is as flexible and dynamic as possible. It will be independent of the police service.

The launch of the new agency has been accompanied by new regulations designed to help police tackle gangsters. These include new regulations to allow criminals to turn Queen’s evidence and secure more lenient sentences or immunity from prosecution in return for informing on their crime bosses.

Financial reporting orders which require criminals to disclose all the details about their financial dealings and disclosure notices which could compel them to cooperate with the law enforcement agencies will also be introduced.

Mr Blair said the aim was to make life as difficult as possible for organised criminal gangs and he vowed to introduce even tougher powers if necessary. "If we find we need to go further, we will go further," he pledged. "There is nothing that should come before the basic liberty of the people in this country to be free from the tyranny of this kind of organised crime. "

After the Downing Street launch, Mr Blair and Mr Clarke attended a photocall at Wellington Barracks, where they inspected a Porsche and a BMW confiscated under the Proceeds of Crime Act. The boots of the cars - both confiscated by Leicester police - were stuffed with confiscated jewellery, faked passports and a range of confiscated guns, including revolvers, self-loading and fully automatic pistols.

The Home Secretary and the Prime Minister were accompanied by Bill Hughes, the former head of the National Crime Squad who is director-general of the new agency. Soca will be chaired by Sir Stephen Lander, former head of MI5, the UK's internal security agency.

One of Soca's first tasks will be to build up a more comprehensive intelligence picture about the organised criminal networks operating in the UK. Mr Hughes admitted "we are not as aware as we should be" about the full picture of organised crime and Soca would bring together the intelligence and the executive aspect of law enforcement to change this.

"How will we know when we have been successful?" he asked. "Criminals should start to find the UK an extremely unattractive market."

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