THE only actor on the set of Outlander who could speak Gaelic was a Sassenach, Glasgow-based language coach Àdhamh Ó Broin has revealed.

Àdhamh was drafted in to make sure every vowel, accent and intonation was perfect on the US time-travel blockbuster, that is about to go into production for a second series in Cumbernauld.

No easy feat among three Englishmen and three lowland Scots, he says.

Only Irish actress Catriona Balfe, who plays English 1940s' nurse Clare Randall, could say any more than Ciamar a tha thu? to Àdhamh, which is Gaelic for Adam.

But after his five-week boot camp, the cast, including Scots stars Graham McTavish and Gary Lewis, had mastered the notoriously difficult language well enough to chat off camera.

He has particular praise for Dumfries-born actor Sam Heughan, who plays main character Jamie Fraser, and who has melted female hearts worldwide with his tender Gaelic endearments to Claire.

"The person who could hold it up consistently and dish out the acting while doing it was Sam," says Àdhamh.

"When he got into his flow, he was absolutely unstoppable. He was just glorious.

"Sam and Duncan (Lacroix) got to the stage where if you sat them down, they could hold a conversation for 30 to 40 seconds.

"I was taking three Englishmen and three lowland Scots from absolutely nothing to them being relaxed enough to deliver the lines and 90 per cent of the time they kicked it out of the park.

"The hardest thing was intonation, getting them to put emphasis on the right parts of the speech.

"And I mean I was really getting on to the guys. Getting them to repeat things dozens of times and never once was there a complaint. I thought how lucky am I, I've got six boys here and not a diva among them."

The Gaelic is not subtitled in the Starz series because producer Ron Moore wanted the viewers - most of whom would be non-Gaelic speakers - to get a sense of how it feels for Claire, who is transported from 1940s through standing stones to 18th-century Scotland.

He said: "I said to Ron, I assume it will be subtitled and he said no, 'I want everyone to see it through Claire's eyes'. He wanted theAmerican audience to be genuinely bamboozled by it.

"It's a bold move, to intentionally confuse American audiences because they like things straightforward."

Amazingly, Scotstoun-based Àdhamh, a married dad-of-four, is not a native Gaelic speaker. Born in Argyle, he went to school in Glasgow and learned the language at council-run classes.

He is only half-joking when he says he has ambitions to be "the finest Scottish Gaelic speaker in the world."

He praised US author Diana Gabaldon for "holding a magnifying glass" up to Scottish Gaelic culture and is just back from a tour of Outlander fan groups in cities including Seattle, where, he says, there is an insatiable demand for the language.

He said: "We needed the magnifying glass from the outside and now the rest of the world is looking at us, saying what are young going to do next? How are you going to meet the demand for knowledge and appreciation of your culture.

"Some people have said the Gaelic in it is all wrong. This woman went to the trouble off giving the language its place in these books, which has barely been done before and you want to moan about a couple of spelling mistakes. She's from Arizona.

"The thing that grates is people without a word of the language or of Scots get on their high horse about Scottish culture and how people are portraying it.

"Get to grips with your own culture, then can criticise someone else's.

"They have a passion for it over there. They are giving us a showing-up in many ways."