DEREK RIDDELL is delighted to be starring in Frankie, BBC1's drama featuring the hugely excitable Bristol nurse, with the Glasgow-born actor playing her colleague and close pal.

The "unknown" is currently enjoying a run in the West End, working alongside showbiz royalty in the form of Dame Judi Dench and the new young Prince of Theatre, Ben Whishaw, in Peter and Alice.

However Derek, who appeared in am-dram as a youngster, certainly doesn't accept he's arrived in terms of acting success.

He's not a man whose cup is running over with over-confidence.

"I was quite shy, as a child," he said. "I know people never believe that of an actor, but it's absolutely true. A lot of actors are shy and need to be someone else.

"I've questioned lots of times whether or not I should be doing it. But when I'm working I never say 'I'm never doing this again.'

"Every actor enjoys working, rather than not acting.

"You do a job then you do another, and then you may not work for a while. Some work from drama school right on through. Some don't."

Derek's track record however speaks for itself.

Straight out of drama college he landed the lead role in BBC Scotland drama Strathblair and he's gone on to appear in TV work such as No Angels, Ripper Street and The Book Group.

But he's also become an international success story, thanks to his role in Ugly Betty, in which he played Ashley Jensen's recovering alcoholic husband, Stuart.

Was he wary of stepping into such a high-profile role?

"I'd worked with Ashley in The Big Picnic in Glasgow, (1994) and we'd known each other for years so that helped," he says in soft voice.

"I'm sure she put in a bit of a word for me. But my first day on Ugly Betty was one of the most bizarre I've ever had.

"I was hanging about the lot with Ashley and Victoria and Brooklyn Beckham were there.

"Then David arrived in a big black Range Rover. And we were in different corners, sitting doing nothing when Ashley suggested we go speak to them. So we had a chat with David, and he was very nice.

"But it was midnight before I got on set to shoot my scene; in America you work until the days' filming is finished."

The first Betty line he had to utter was a heap of nonsense, he admits.

"The writers had come up with something that was supposed to sound vaguely Scottish," he said.

"They did that often with Ashley and she'd change it into something realistic.

"But I didn't know this and the line I had (he played a drunk wastrel) was 'Can you help a bloke who's down to his last floggin?'"

Former Hutchesons' Grammar School pupil Derek had a dilemma; should he argue with the director about his very first line in his first internationally successful show? No. He did his best to flog the line to the world.

"All I could think about was everybody back in Scotland thinking 'Whit did he just say?'" he said.

The father-of-twins – his partner is actress partner Frances Corrigan – enjoyed the two-year stint in LA but 'felt Stuart was too heavy for the programme'.

"I'd read the scripts to find out if I were dying that week because they didn't seem to know what to do with my character. It was slightly predictable the Scottish ex-husband was an ex-alcoholic."

Derek, who'd embarked upon a business degree but abandoned the honours year to study drama, tested the waters of acting possibility while in Hollywood but he found the casting sessions demanding.

"I'd ask to go up for the roles of the leading man's pal," he said. Even when the lead was described in the script as 'an ordinary guy' they never looked ordinary.

"They always looked like Matthew Fox out of Lost. I figured I'd stand a better chance as 'The Mate'."

COMING home was a culture shock. He said: "I remember taking a train from Glasgow to Edinburgh after a football match and hearing all this shouting and swearing, the usual stuff.

"Nothing bad. But it came as such a surprise because in two years living in LA I hadn't heard anyone raise their voice.

"To be honest, LA was nice, but 'nice' becomes a bit dull after a while."

Had acting success ever taken him on the road to excess? Wild, drug-hazed nights in Hollywood?

"Never. And I'd hate to think I would act that way. I'm not the sort to get over confident or feel secure ... in anything I suppose."

l Frankie, BBC1, Tuesdays at 9pm. Peter and Alice, the Noel Coward Theatre, London, until June 1.