The HMS Montrose "really didn't have much chance of having an impact on the scene," said Philip Diacon, head of Dryad Global, a London-based shipping risk management company.

Diacon refused to discuss how he obtained the audio of Friday's high-seas drama over the Stena Impero.

But he said the entire exchange was conducted over an open channel -- number 16 -- which is used globally by military and commercial vessels to send out calls.

Britain's helplessness in the situation has seen Foreign Secretary Jeremy Hunt get accused of devoting too much time to his ongoing UK leadership bid and not enough to his diplomatic duties.

Diacon agreed that "this obviously did, to an extent, catch the UK by surprise".

"The shipping industry was not really prepared for this."

Diacon said his global clients were starting to look for alternatives to using British-flagged vessels in the Gulf.

Almost a fifth of the world's oil passes through the 21-mile (33-kilometre) strait between Iran to the north and the United Arab Emirates to the south.

"Normally it's the British-flagged, US-flagged and Saudi-interest vessels that are the most likely to be targeted," Diacon said.

He said it takes at least a month for shippers to complete the paperwork needed to have their vessels registered under a different national flag.

He said most were now looking to China -- a major player in the Gulf region that Iran views as an important ally.

"We are starting to see talk of moving to Chinese-flagged vessels," said Diacon.

"Oil will continue to flow. The Iranians have no interests in disrupting other nations."

- 'Warships are not the answer' -

Diacon pointed out that about a hundred tankers go through the Strait of Hormuz in any 24-hour period and that accompanying each one was simply impossible at this stage.

The United States is pressing other nations to join it in a proposed Gulf convoy system that was last used during the "Tanker War" of the late 1980s.

But Britain and other European governments are cautious.

They fear the convoys could spark a broader military operation that could result in all-out war.

"All governments will be under extreme pressure now to do something," Diacon said.

But "you need a lot of assets to do it effectively and you need buy-in from nations to support it," he said.

"Warships are not the answer."