Traders openly selling illegal animal products such as ivory in UK shops cannot be arrested because of a government "slip-up", it has emerged.
Ivory, believed to be from elephants, was seized in UK raids
Primary legislation banning the trade went through last year.
But a spokesman for the Department for Environment, Food and Rural Affairs said "secondary legislation" was needed for it to be able to prosecute.
The impasse emerged after £85,000 of ivory and tortoiseshell goods were seized in police raids last week.
New powers and penalties were approved by parliament in November 2003 to increase the maximum prison sentence for wildlife trafficking from two to five years, and to give police the power of arrest for such crimes.
But according to the WWF and the International Fund for Animal Welfare, Defra has consistently failed to amend the existing regulations to incorporate the new law.
This means little can be done to stop the sales of goods made from illegal materials, they say.
"Had Defra implemented these powers, more criminal suspects would now be behind bars, acting as a deterrent to others," said Jenny Hawley of Ifaw.
"The department's failure to act over the last 12 months simply ignores the will of Parliament and sends a clear message to wildlife smugglers around the world that it's 'business as usual' in the UK."
David Cowdrey, director of the WWF's wildlife trade campaign, said it was a
"complete embarrassment" that Defra had failed to act.
"They really need to pull their finger out," he added.
"We think of ourselves as a nation of animal lovers and yet we are still trading in the world's most endangered species."
Officers were unable to hold suspects for questioning so it would be very difficult to obtain statements, Mr Cowdrey said.
"All they can do is politely ask them to come up to the police station for interview," he added. "It's making a mockery of justice."
Legislation banning the trade went through last year as part of the Criminal Justice Bill.
But a Defra spokesman said the department would soon be consulting on secondary legislation.
"We are aware of the situation and want to act as soon as possible."
The operation on 15 November was launched after it was discovered that a number of shops in central London were openly offering the banned goods for sale.
Three shops in the capital and a manufacturing plant in Gloucestershire were raided but there were no arrests.
As well as the banned goods worth £85,000, police seized 80kg of unworked ivory.
A Scotland Yard spokesman said this was believed to be elephant ivory and was being examined.