The Gavin & Stacey actor is currently rehearsing for the play Entertaining Mr Sloane, in which he plays the title role, but confessed that the experience has been a "real shock to the system".
He told The Guardian: "TV's so quick, you make a choice and you do it, and if the director thinks it's wrong then you make another choice and you do it, and that's it.
"This is a really complex process and discipline. It's a real shock to the system. The first few days of rehearsal were like being hit by a bus."
However, Horne insisted that he is still enjoying the role as it is a completely different character to Gavin Shipman.
"Gavin is a very sort of straight, heterosexual man, albeit a sweet one," he noted. "And this is a bit of a movement on, where my character will f**k anything that moves. That's quite an interesting thing to play."