Mr Pearson criticised staffing levels at the agency

Graeme Pearson, the Scottish Crime and Drug Enforcement Agency's (SCDEA) director general, recently said he was leaving his post two years early.

He told BBC Scotland that the organisation, which tackles organised crime and drug trafficking, is hampered by bureaucracy.

The Scottish Government praised Mr Pearson's time in the job.

The former deputy chief constable of Strathclyde Police accused Scotland's police forces of refusing to release experienced officers for anti-drug campaigns.

He said the SCDEA had never been fully staffed in his time there.

That shortage of staff, which we have the money to pay for, has been difficult to manage over that period Graeme Pearson SCDEA director general

"I wanted to be sure that the agency was in a good position to obtain full resource support from the eight forces," Mr Pearson said.

"It's never achieved its full allocation of staff, for instance, from the eight chief constables in its seven years.

"That shortage of staff, which we have the money to pay for, has been difficult to manage over that period."

Mr Pearson added that he had wanted a strong vibrant and independent agency.

A Scottish Government spokeswoman praised Mr Pearson's "substantial personal contribution" to the fight against serious and organised crime.

"The SCDEA has been strengthened in recent years by putting it on a statutory footing with new powers and functions, including for the first time the ability to directly recruit its own officers and authorise the full range of covert investigatory powers," she said.

"That is the strong and dynamic crime fighting organisation he leaves."

Mr Pearson took up the job in March 2004 and was not due to step down until 2010.