FRAUDSTERS have scammed a Scottish blue chip company of £18million after posing as its boss on the phone.

The criminals - believed to be international - fooled a senior executive at the firm into transferring the money to a foreign bank account.

Their telephone heist, thought to be one of the biggest thefts ever attempted in Scotland, was one of what very senior police sources believe is the latest of a series of sophisticated cons.

The company targeted, which cannot be named for legal reasons, hopes to get its money back after elite financial crime detectives at Police Scotland tracked it down overseas.

But police are investigating two similar telephone scams - a scaled-up corporate version of recent "vishing" phone frauds against individual bank customers - involving tens of thousands of missing euros.

And officers fear other companies have been targeted - successfully or unsuccessfully - but are not telling authorities because they want to avoid the reputational damage of being seen to be duped.

Detective Chief Superintendent Gerry McLean, the head of organised crime and counter-terrorism at Police Scotland, stressed the companies known to be at risk were huge - as was the potential damage to their shareholders and employees.

He said: "We are talking about big international companies that are household names."

In an unusual step, Mr McLean and senior colleagues are describing the scam in the hope that major businesses will be prepared for such attacks.

Detective Chief Inspector Kenny Thomson of Police Scotland's Economic Crime and Financial Investigation Unit said: "In one case the amount involved was £18m.

"We are talking about vast amounts of money. But the way the crime works is similar to a vishing scam.

"The companies targeted appear to be the Scottish subsidiaries of international businesses. Generally, a finance person will get the call from someone saying they are the chief exec. 'You have never met me before,' the person will say, 'but you know my name, don’t you?

"The caller will then say that he has a 'hush-hush' project to discuss, an acquisition or business deal. 'You can’t tell anybody about it,' the caller will say, 'but I need you to move money straight away'."

Mr Thomson said such calls were repeated - usually at time when the global head office was closed - with ever more pressure piled on to the Scottish official.

Police are currently trying to identify other Scottish-based victims. They do know where the money is being transferred to - accounts in North Africa or the Far East before it is "starbursted", distributed through myriad banks and lost forever in a matter of seconds.

Police only managed to get the £18m frozen after acting very quickly. That money has still to be returned and is subject to a major overseas criminal investigation. Mr Thomson said: "Hopefully, the company at the end o the day won’t lose anything. However, we have another case on the go just now which was in the tens of thousands of euros.

"It is not purely a Scottish problem. It is happening across the UK."

There are three such Scottish cases under investigation over the last four-to-five months. Police don't know if they are connected.

Mr Thomson underline just how sophisticated the fraudsters are.

He said: "You would think people would have sussed.

"But these fraudsters are very plausible convincing.

"It is easy to find out which companies have Scottish branches. The callers use the company jargon and they play play on time differences and pressure.

"So the message we want to get out is to be aware, to ask the questions and do the due diligence when pressure is put on you."

Police believe companies should be training staff to know what the rules and regulations are for extra-ordinary transfers. "There should be extra checks before anyone moves tens of millions of pounds," said Mr Thomson, a former bank manager.