French police boarded the train and hauled off the unidentified man in his forties in Lille, France, where the service made an emergency stop.
He was then surrounded by at least eight uniformed officers, before being stranded when the train resumed its journey to England.
“I’ve done nothing wrong and respect all coronavirus rules – this is absolutely outrageous,” he said, as he was led away in front of other stunned passengers on Thursday afternoon.
He added: “I have absolutely no idea what this is all about, except that a Eurostar staff member has taken a very strong dislike to me, and accused me of not wearing the right type of mask.
“Now I’m going to be left alone in France, when all I wanted to do is get home from a work trip. This is very cruel treatment. We should all be getting on, not treating each other like this.”
The female Eurostar manager – who remained on the train after the man was taken into custody – confirmed she had reported him for wearing the “wrong type of mask”.
Asked why the man had been forced off the train, one of the Lille police officers confirmed he had been arrested, and said: “We don’t know why, we’ll have to find out.”
The drama unfolded soon after Eurostar 9031 left Paris Gare du Nord on time at 1.13pm French time on Wednesday.
Within minutes of departure, the Eurostar manager got into a heated argument with the man.
She accused him of not complying with health and safety regulations, and said the black mask he was wearing was not appropriate.
The businessman then replaced his black mask with a standard blue one provided by another passenger. He apologised, and appeared to have escaped any further action.
But when the train got to Lille it made an unscheduled stop, and three armed officers boarded while others waiting on the platform.
“It was ridiculous,” said another passenger, a 32-year-old woman from London.
“He was actually being very reasonable, and not swearing or acting in any kind of disruptive way at all – everybody else was on his side, but he was marched off and we didn’t see him again.”
Eurostar was approached for comment on Thursday night, but by Friday morning had still not responded to enquiries about the arrest.