Scrap dealers helped build a case against four cemetery workers in Prince George's County, Md.
The decrease was due to targeting thieves and rogue scrap dealers, a police spokesman said.
Devon and Cornwall Police said a national campaign to make scrap dealers aware of illegal metal had also helped.
Devon and Cornwall Police said the scheme was working and was making scrap dealers more aware of the trade in illegal metal.
"Although we can't be certain, there is a strong possibility that the thieves are targeting the golf clubs in order to sell the metal to scrap dealers, " he said.
Ian Hetherington, head of the British Metals Recycling Association, said there was a problem with the number of illegal scrap dealers in the UK which could be as many as 900.
BBC: Rail cable theft: Up to eight cases a day, MPs are told
The Act requires all scrap metal dealers to be registered with their local authority and obliges them to maintain records of all transactions relating to scrap metal received and processed.
"Scrap metal dealers know they couldn't have come by them honestly, " he says.
It comes ahead of a bill, tabled by Richard Ottaway MP, which would see licensing for scrap metal dealers.
The Scrap Metal Dealers Bill aims to reform the industry and tackle what Mr Ottaway calls "outdated legislation" from 1964.
They also want annual licensing of scrap metal dealers similar to pubs.
First up is the report stage of the Scrap Metal Dealers Bill.
The British Metals Recycling Association has been supporting the Scrap Metal Dealers Bill, saying a cash ban alone will not reduce metal theft.
Make it harder for scrap metal dealers to sell stolen metals.
Topping the bill is the Conservative Richard Ottaway's Scrap Metal Dealers Bill, which tightens the regulations to make it harder for thieves to sell on looted metal.
The Scrap Metal Dealers Act 2013, passed by Parliament earlier this year and due to come into force in the autumn, would provide a further boost, he added.
Labour have urged ministers to toughen regulation by licensing scrap metal dealers, making it easier to close down rogue operators and to examine a ban on cash transactions.
BBC: Rail cable theft: Up to eight cases a day, MPs are told
Det Insp Cleland added the number of metal thefts had also been cut due to another initiative called operation Tornado "a code of conduct for the scrap metal dealers".
British Transport Police were also involved in the operation and visited 11 scrap metal dealers north and south of the border as part of their ongoing commitment to tackling metal theft.
Mrs May told MPs the government was working closely with the Association of Chief Police Officers (Acpo) to see what legislative changes might be needed to the Scrap Metal Dealers Act 1964.
Mr Brokenshire said the existing 1964 Scrap Metal Dealers Act was "no longer fit for purpose" and needed to be revised, but stressed the need to combine that with further enforcement and better intelligence.
"Over the past six to eight months, we've been doing some work with local communities and scrap metal dealers which has enabled us to see a substantial decrease in the number of offences, " he said.
There is a panoply of amendments, one of which addresses the issue of cash payments by scrap metal dealers, courtesy of Lords Bradshaw and Faulkner of Worcester, who had tried to put a clause on this issue into the Protection of Freedoms Bill.
Those selling scrap metal to dealers did not have to provide proof of their identity and, unless this was tightened, it would be "almost impossible" to charge someone if the material was obtained illegally.
BBC: Rail cable theft: Up to eight cases a day, MPs are told
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