The Scotland Office and transport minister said he had been impressed by the results of trials of the technology currently being carried out in London.

Since the launch of a British Transport Police operation there in February, 10,000 people have been scanned and 107 arrests made. Almost 70 weapons have been recovered.

“Most knives are all too easy to hide, so the new initiative uses full-body scanners and hand-held scanners to detect whether someone is carrying a knife in the first place,” said the minister.

“The trials undertaken by the BTP have shown some good results.

“I am pleased to say that the trial will be rolled out nationally — including to Edinburgh, Glasgow and Dundee – this year, as part of the Safer Scotland campaign.”

Local police commanders will be responsible for deciding where the metal detectors are used, based on crime levels.

The minister said he believed the scanners would have a “significant impact”, although they need to go hand-in-hand with other measures.

The announcement comes as new figures showed Scotland’s railways are safer than ever, with violent crime being cut dramatically over the past year.

Assaults on passengers dropped by 34% to 202 offences in the year to March 31, compared to 306 the previous year.

Offenders were detected in around two-thirds of cases — well above the target set by the force and the train operating companies.

It was also stressed that knife-related incidents on trains around one for every four million passengers.