Bogus council workmen have been touring the Scottish countryside stealing road signs that have become a valuable commodity as a result of the worldwide shortage of metal.

In the first of a spate of metal thefts across the UK, 16 aluminium signs, including Stop, Give Way and Dangerous Bends were stolen in Netherley, Aberdeenshire, after two men wearing reflective jackets and trousers were seen acting suspiciously in the area at the start of the week.

The second incident on Wednesday night involved a break-in to premises on Station Road, Fordoun, when a large quantity of stainless steel parts and accessories were stolen, while on the same evening a large stainless steel bowl was taken from premises on Badentoy Way, Badentoy Industrial Estate, Portlethen.

The property stolen in each of the three thefts is valued at a four-figure sum and it is thought the culprits may have used a large vehicle to remove the items.

Lead and copper have become increasingly valuable because of a world shortage coupled with high demands in China, India and Dubai, and in the past two years the fluctuating price of copper has risen by 30%.

The north-east appears to be the worst affected area of Scotland with only Tayside police reporting a similar, although sporadic, problem with metal theft.

More than 50 thefts of lead and copper have been reported to Grampian Police in the last three months and they are warning that rooftop robberies could result in serious injury.

The total value stolen in the incidents in the force area for the three months to the end of October was nearly £100,000.

In one incident, a cancer care centre ended up with a £3000 bill because of damage after lead was stripped from its roof. Police are also investigating a number of high-value thefts of other types of metals from industrial premises connected to the oil industry.

Across Scotland, hundreds of drain covers have disappeared, a statue of Olympic champion Steve Ovett was stolen in Brighton, and in some cases thieves have cut through live electricity and gas mains to steal metal.

Scrap dealers in Aberdeen are helping to clamp down on the problem. David McAllister, a partner with Panda Rosa Metals in Aberdeenshire, said: "We are looking to eliminate lead theft by refusing to accept deliveries from certain individuals. People who turn up expecting to make money from stolen materials will not be accepted or tolerated."

An Aberdeenshire Council spokesman said: "Whoever took these signs has no consideration for motorists' safety and we would urge road users to take extra care on this route while the signs are replaced."