Hugh kicks up a Stink.
He is almost unrecognisable with his shabby clothes, busy grey beard and unkempt hair. He's playing a homeless tramp in Mr Stink, an adaptation of David Walliam's children's book shown on BBC1 on Sunday.
It's a world away from his role as Lord Robert Grantham in ITV1's Downton Abbey.
"It took an hour and a half in makeup," the actor announces proudly, adding "Our make-up director had great fun getting just the right consistency of snot to embed in my moustache."
It's enough to make the Dowager Duchess choke on her afternoon tea!
Not only that, but Mr Stink is followed everywhere he goes by a special effects haze of putrid smell. When you're sleeping rough, personal hygiene standards tend to slip, but Hugh says there's another reason why Mr Stink smells as he does. "He's very much an outsider, and this wall of aroma around him keeps people away. He doesn't want people to get too close."
However, much to his suspicion, a 12-year-old girl called Chloe (played by Nell Tiger Free) decides to befriend Mr Stink.
"Chloe is an outsider, she's teased at school, she's not one of the gang. Chloe gets past the stink because she understands that he is on his own as she is. Chloe sees a kindred spirit and they form a bond," explains Hugh.
The book has been adapted for the screen by Walliams himself, who also appears as the Prime Minister.
"There are lots of fart and poo jokes in a very David Walliams way," says Hugh.
"He's in our faces most of the year, and in this case he's in my face," he jokes of the Britain's Got Talent judge.
Another key member of the cast is BGT winner Pudsey. David brought the talented dog in to play Mr Stink's beloved companion Duchess.
No stranger to working with dogs on set, Hugh knew how to butter up Pudsey in the same way he has to butter up Labrador Isis on the set of Downton Abbey. "Put it this way, they both love treats," he says. "They'll do anything for treats - a bit like actors really."
Of course, Hugh is much better dressed as Lord Grantham in Downton Abbey, but there was a day when he got as dirty and smelly as Mr Stink.
That was during a hunting scene for the Christmas Day special, filmed in Scotland in late summer.
His co-star Peter Egan, who plays Lord Flintshire, reveals: "We had to go on our bellies and it was muddy and full of animal poo.
is. a "Of course when you see it, it will be 30 seconds but we had eight hours of it!" Hugh reveals that, like millions of other viewers, he will be sitting down with his family to watch Downton on Christmas Day.
the appears "You only see your bits while you're filming so it's lovely to see the whole thing put together," he says.
in a and of And as for his other duties on Christmas Day, Hugh says his main responsibility is to "keep out the way".
BGT companion on Labrador Laughing, he adds: "And I open the wine. I'm also religious about leaving out a mince pie and a glass of sherry. I get pathetically excited about Father Christmas coming!" - a
ROUGHING IT: Hugh with co-star Nell Tiger Free, and, above with David Walliams