It is only legal to sell ivory that dates from before June 1947 and is subsequently classed as "antique". However, it has always been difficult to police the huge illegal trade in ivory because it has been impossible to work out accurately the age of specimens.
There have even been signs that the illegal trade in ivory has increased in recent years.
Now Dr Ross McEwing, a forensic zoologist at the Royal Zoological Society of Scotland, has come up with a solution.
His technique, like traditional methods for ageing ancient relics, tests levels of the naturally occurring isotope carbon 14. But McEwing's method is novel in taking advantage of the glut of carbon 14 that entered the atmosphere during nuclear weapons testing in the 1950s and 1960s and was absorbed by the world's animals and plants.
This means elephants alive before 1947 can be identified by their low levels of carbon 14. And although nuclear weapons testing stopped with the Limited Test Ban Treaty in 1963, levels of carbon 14 in the atmosphere will not return to pre-testing levels for the next few decades.
McEwing, the only specialist of his kind in the UK, has been granted 28,000 funding from the Department of Environment, Food and Rural Affairs (Defra) to refine the technique.
For six months next year he will test samples of ivory from UK museums – mainly the Royal Museum of Scotland, where Dr Andrew Kitchener, curator of mammals and birds, is helping with the research.
Only samples from the museums for which the age is known will be tested for carbon 14 levels, to provide the evidence needed to show the technique is reliable.
This will be carried out at the Scottish Universities Environmental Research Centre in East Kilbride, which has a machine that can test for carbon 14.
Once this evidence has been acquired, McEwing is confident it will be used to provide evidence of illegal ivory trading in court. "There is still a lot of ivory coming into Europe and people are selling it as antique when it is not," said McEwing. "The biggest problem is how do we prove that it is not antique, when the seller says it is."
Until now, the only option has been to send samples to museums where experts tried to work out from the appearance of the ivory whether or not it was legal, from signs such as how yellow it appeared.
However, they could not say definitively how old the ivory was, meaning their evidence would not stand up in court.
McEwing was approached for suggestions of other techniques that might work while he was chairman of the Partnership for Action Against Wildlife Crime forensic working group.
"I was aware of this ability to detect nuclear weapons testing, which was carried out between about 1950 and 1960," he said. "This was a global phenomenon and the carbon 14 was being absorbed by plants and animals."
A tiny sample – little more than a speck of dust – is taken from the ivory sample to be tested. A very similar technique based on chemical markers is employed for testing the age of human remains using teeth.
"It will work," said McEwing. "The technique already works for humans and ivory is just a growing tooth."
McEwing hopes in the future ivory confiscated by the UK Border Agency, or from shops and stalls where it is being described as antique, can be tested using the technique to enable successful prosecutions where it is being sold illegally, although this will be expensive, at a cost of 300 a test.
"This will have a huge impact on the sale of illegal ivory in the UK because they won't now be able to hide behind the word antique," he said.
The technique also has the potential to be used for testing the age of rhinoceros horn and turtle shells, which are also traded illegally.
A worldwide ivory trade ban was introduced by the Convention for International Trade in Endangered Species in 1989.
At its height, the ivory trade was driving the poaching of an estimated 100,000 African elephants a year for their tusks, putting the species at risk.