An elite new agency set up to tackle organised crime must be "ruthless", the prime minister has said.
Mr Blair said the police had to be as organised as the criminals
Tony Blair hinted the standard of proof in organised crime cases may need to be lowered so that it is easier for police to secure convictions.
Mr Blair was speaking at the launch of the Serious Organised Crime Agency (SOCA) which will combat crimes like people smuggling and drug trafficking.
The crime-fighting force has been dubbed Britain's FBI.
The agency is a merger of the National Crime Squad, the National Criminal Intelligence Service and the investigative branches of Customs and Excise and the Home Office Immigration Service.
It will not deal with terrorism or murder cases.
Visiting the National Hi-Tech Crime Unit in London's Docklands on Monday, the prime minister said: "We're not going to beat organised crime if we simply work in
the way we worked 15 or 20 years ago."
"We've got to be hard, efficient and, if necessary, ruthless."
He added that it was his "impression" that sometimes "the system is
struggling against a presumption that you treat these crimes like every other
type of crime and that you build up cases beyond reasonable doubt".
"I think we have got to look at this."
The prime minister also appeared to suggest that criminals may be required to explain how they had
generated their wealth.
The new agency, which marks the biggest shake-up of policing structure since 1964 when the 43 force areas were drawn up, is not expected to be operational until 2006.
It will employ as many as 5,000 agents to fight the big business end of organised crime, which individual forces find difficult to tackle on their own.
The Metropolitan Police welcomed the new agency.
Assistant Commissioner Tarique Ghaffur said: "London's communities are blighted by organised criminal networks, which have a national and international dimension.
"We will work with the agency to ensure there is a faster and more flexible approach to dealing with this menace".
Professor Gloria Laycock, of the Jill Dando Crime Institute, said that working as a single body will alleviate "rivalries between the various different agencies fighting Britain's crime".
"Criminals take opportunities as they arise," she told BBC News.
"Organised criminals move very quickly. We need to get much quicker in our reactions."
However there are concerns comparisons between the new agency and the American FBI could go too far.
Jan Berry, the national chairman of the Police Federation of England and Wales which represents rank and file officers, said: "Elitism has no place in British policing.
"I am worried that we will see a skills loss across the 43 police forces in England and Wales, with the cream of the crop being taken to fill places in this new agency."
NCIS: 1,200 staff, £93m budget
NCS: 1,750 staff, £130m budget
Customs and Excise: 1,850 staff, £1bn budget
Home Office Immigration Service: 60 staff
And the Association of Chief Police Officers wants the government to ensure the agency avoids US-style arguments between "feds" and local police.
The agency will have the power to make its own arrests, but will also provide intelligence to a local force and leave the prosecution to them.
It is hoped a single national body will find it easier to deal with gangs who might operate in Europe as well as the UK, for example people smugglers.
These gangs are often involved in crimes such as trafficking sex slaves or child pornography.
The new agency is likely to have civilian investigators such as accountants, financial experts and computer experts to unravel paper trails and complex internet fraud.