The Met's unit has a specialist pro-active role in tracking paedophiles

Mike Hames, who was the detective superintendent in charge of the specialist unit from 1989 to 1994, said he was "appalled" at the decision to rotate staff.

It is designed to alleviate the pressure on officers who have to deal with some of the most inhumane and degrading crimes.

But far from images of abused children putting the officers under stress, Mr Hames argues the upheaval caused by losing their best officers will make their job more difficult than ever.

"If this policy - of moving the top nine people - goes through it will destroy the unit because there are only 12 people there at the start."

He said it would take at least 18 months to train an officer and training them would tie up the remaining experienced staff.

There is no more pressure than there is in dealing with a murder

"The work is going to come to a stop," he said.

"The unit is a centre of excellence and all those contacts would be gone."

Mr Hames said "in 20 years" he had never heard of an officer suffering as a result of working in this area.

"There is no more pressure than there is in dealing with a murder," he said.

"The officers are not sitting day after day watching obscene pictures of children."

Highly skilled

But he said it is "very exacting" and "precise".

"They have to interview suspects differently from, say, a burglar - they have different motivation.

"When you interview a paedophile in custody or treatment or prison, you talk to them about their motivation. You talk to them at length about what they did to ensnare children."

Officers also spend time investigating their contacts, family relationships, trying to identify abused children and liaising with international agencies like Interpol.

"You put the whole suspect's life under the microscope."

Let's not mess around any more - either we're serious about it or we're not

Mr Hames said there was a desperate need for more officers in the team, particularly as they wade through as many as 1,000 suspects' names from Operation Ore - the nationwide investigation into internet child porn.

"Ten blokes aren't going to get very far with these," he said.

""When I was there I had 16 and I was always screaming for double the number.

"Let's not mess around any more. Either we're serious about it or we're not."