Drug trafficking "poses a major threat to the UK" according to a new police report.

The warning came as the National Criminal Intelligence Service published its threat assessment of serious and organised crime.

It added that the City has become an important destination for dirty money from organised crime.

But police forces said that the key threats to the UK were being tackled with increasing success, partly through improved intelligence gathering and tougher new laws.

Peter Hampson, director general of the NCIS, said that "the impact of serious and organised crime is felt by everyone in the UK".

"The trades in drugs, people and illicit goods, the related crime and violence, and the corruption of people from all walks of life cause damage to families , communities and society in general," he said.

"By raising public awareness, we hope to make it harder for serious and organised criminals to create new victims and to conduct their criminal business."

Hampson also warned that serious and organised criminals are "determined, ruthless and quick to adapt to threats and opportunities".

"We must show them that we are more determined, more ruthless and quicker on our feet, and the key to this is good intelligence," he added.

"We need to know who they are, what they are doing and what they are thinking, so that we can frustrate them and bring them to justice."

The law enforcement authorities, which cooperated on the compilation of the report, said the most significant threats to the UK are:

• Class A drugs trafficking (heroin, cocaine powder, crack cocaine and ecstasy)

• Organised immigration crime; fraud (particularly revenue fraud)

• Money laundering; possession and use of firearms; hi-tech crime

• Sex offences against children, including online child abuse

On drugs, the report warned: "By any yardstick, drugs trafficking poses a major threat to the UK."

And with the use of firearms rising, it added that "it would appear that any criminal who wishes to obtain a firearm will have little difficulty doing so, whether a genuine weapon or one that has been reactivated or modified".

"Some serious and organised criminals routinely carry a firearm and certain groups are quick to resort to the actual use of firearms, rather than using them merely to threaten, to enforce drugs debts."

Responding to the report, Home Office minister Hazel Blears said it would "play an important role in helping the government and law enforcement agencies build on the good progress we have made".