The main rail union has sharply criticised Mr Soames for travelling from England to visit Caledonian Sleeper staff today.
The Rail, Maritime and Transport union (RMT) described the two-day trip as “absolutely outrageous”.
Serco, which operates the Scotland-London overnight trains, insisted Mr Soames’ visit to “front-line staff and key workers” was “essential".
He arrived on a Sleeper service this morning from London.
But RMT Scotland organiser Mick Hogg said: “I find that astonishing. It should not be happening.
“There are other managerial colleagues who could deal with that.
“Clearly, he has not been listening and he seems oblivious to the guidance.
“Does he think because he is a senior person in business it is ok for him to travel?”
First Minister Nicola Sturgeon said yesterday: "If you live just south of the Border and you work in an essential job then…that is perfectly legitimate.
"But if you are coming to Scotland and are not covered by those essential purposes, then you potentially would be in breach of the law."
The Scottish Government’s Transport Scotland agency, to whom Serco is answerable as Sleeper operator, said: “We were not aware this visit was happening.
“The Scottish Government advice is absolutely clear – do not travel unless your journey is essential.”
Scottish Labour transport spokesperson Colin Smyth said: “Those who work on our buses, trains and ferries have been heroic in keeping Scotland moving.
“But there is a big difference between the crucial role a train driver plays ensuring their fellow key worker gets to work and a chief executive touring the country.
“I’m not sure what Rupert Soames will have learned on his visits that he couldn’t have done by speaking to front-line staff virtually.
“This incident seems to highlight the confusion caused by the UK Government’s message that people should get back to work.
“The message in Scotland remains ‘Stay at Home except for essential purposes’, and few will see Mr Soames tour as essential.
“Mr Soames’ cavalier attitude to the Stay at Home message can only undermine the fight to control this pandemic.”
Serco declined to say whether Mr Soames would be visiting other parts of Scotland during his trip, but said he would be observing social distancing at all times.
Its spokesman said: “As he has reported on Twitter, Rupert Soames has been visiting a number of front-line staff and key workers during the crisis, essential in his role as chief executive.
“He fiercely defends his decision to show solidarity with front-line workers and believes that hiding at home while others are expected to work in trains, prisons and hospitals is not an appropriate style of leadership.
“He is returning straight back to London on Wednesday, which will allow him to meet the guest services team in Inverness and four Caledonian Sleeper train crews.
“Between times, he is doing permitted activity, job interviews and contract visits.”
Serco said Mr Soames had made other visits in recent weeks to the company’s operations at the Yarl’s Wood Immigration Removal Centre in Bedfordshire and prisons at Thameside in south east London, Dovegate in Staffordshire and Doncaster.
It said he had also visited the Royal London Hospital and the James Cook University Hospital in Middlesborough, drive-through test centres at Chessington in south west London, Oxford and Doncaster, asylum seeker accommodation in Liverpool and call centres in Manchester and Liverpool.
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