THE head of the UK's leading crime-fighting agency has warned that the internet poses today's greatest criminal threat.

Speaking exclusively to The Herald, Keith Bristow, head of the new National Crime Agency (NCA), said criminals do not respect borders and paid tribute to the strong relationship between the agency and Police Scotland.

He visited Scotland last week to speak to MSPs at the request of Justice Secretary Kenny MacAskill, to explain the agency's role and how it will work alongside Police Scotland. The presentation follows concerns raised by senior officers that there was a lack of clarity about its remit.

Asked about the greatest threat to modern policing, Mr Bristow said it was the internet - with both new crimes such as phishing and old crimes such as fraud and child abuse proliferating.

He said: "For law enforcement across the world, the internet, which has been a great power for good, now presents a serious threat. We must police the internet. We need to ensure we have the focus on the internet. That is a very significant focus for us."

Mr Bristow, former chief constable of Warwickshire, has warned criminals they can no longer hide their identities online on what is referred to as the "dark" or "deep" web, where encrypted sites and anonymised networks are used to facilitate drug dealing, fraud, terrorism and illegal pornography.

The NCA recently helped shut down the Silk Road, one of the world's largest websites selling illegal drugs, which branded itself an "anonymous marketplace".

He said: "The hidden internet isn't hidden and your anonymous activity isn't anonymous. We know where you are, what you are doing and we will catch you.

"It is impossible for criminals to completely erase their digital footprint."

The NCA, which was created last month, runs the national cyber-crime unit. It also has the task of targeting the 37,000 high-level gangsters and 5500 crime groups across the UK - including approximately 3500 high-level criminals in Scotland - where it works alongside Police Scotland.

Last month, deputy chief constable Iain Livingstone, one of Scotland's most senior police ­officers, warned the role of the NCA was unclear and that the public needed to know whether the force had "primacy" north of the Border.

Mr Bristow made clear that the director general of the NCA has the power to direct chief police officers in England and Wales, but not in Scotland.

He added that the best way to tackle organised crime and cyber crime was through joint working.

"We are very much a law enforcement agency with a focus on identifying, pursuing and disrupting serious organised criminals," he said. "We want to share the impact of that with the public because we're using public resources and because they're trusting us with these powers. The public needs to be confident that the NCA is working hard with Police Scotland."

He said: "Throughout the build of the agency we have had huge support from Police Scotland and the former SCDEA (Scottish Crime and Drug Enforcement Agency). We are a UK-wide organisation and I will continue to spend some of my time in Scotland. The relationship with Police Scotland is very important in ensuring we have a serious impact on organised criminals in Scotland."