Wellington, Oct 7 NZPA - An explosive and dangerous "shake-and-bake" method of manufacturing the drug P in a two litre juice container may not catch on in New Zealand, experts on illicit drugs say.

A forensic scientist at Environmental Science and Research Ltd (ESR), Keith Bedford said yesterday one of the distinctive features of the "clan lab" scene in New Zealand was the application of kiwi ingenuity.

But both the key chemicals used in the "shake-and-bake" method were dangerous: anhydrous ammonia was a gas compressed to the point where it liquified, and lithium was a metal which could be very volatile, said Dr Bedford.

The method has been spreading through American states as authorities there clamp down on access to cold and flu remedies containing pseudoephedrine which clandestine laboratories use in manufacturing methamphetamine.

It means a small batch of P can be produced with just a handful of tablets, in a small space such as the back seat of a car or a toilet stall.

But the method is also dangerous, with many people killed and serious fires triggered.

Mike Sabin, a former police detective who runs MethCon Group, a specialist methamphetamine and drug awareness educator, said putting a few handfuls of cold pills in a drink bottle with noxious chemicals, and shaking it could produce one of the world's most addictive drugs -- or a nasty fire.

"It's a controlled explosion, in a plastic bottle: you put lithium and water together and you have fire," he said. "It can all go bad quite quickly"

The existing methods used in New Zealand were safer, and equally effective for a "Ma and Pa" style manufacturing operation.

"There's only been two labs that have used ... anhydrous ammonia and lithium," said Mr Sabin. "That's two out of the 1400-odd labs that have been found".

Dr Bedford said the ingenuity of local bakers meant they were quick to find easier and simple ways of doing things.

There were many different approaches to manufacturing P from pseudoephedrine or ephedrine - the favoured method in NZ clan labs involved hydriodic acid (CRCT) and red phosphorus, because it was relatively simple.

Other methods used phenyl-2-propanone,(CRCT) or benylchloride.

But even if people did try to use lithium in liquid ammonia, they would still required access to pseudoephedrine or ephedrine.

Dr Bedford said restricting availability of cold remedies containing pseudoephedrine would put a constraint on clan labs regardless of which method of manufacture they used.

The shake-and-bake approach gained popularity in the USA after purchasers of pseudoephedrine were required to register their purchase. This hit the makers using elaborate labs to make bigger batches from hundreds of tablets at a time.