Hugh Bonneville has admitted it is easy to find humour in the BBC security system, because it is so ridiculously complicated.
The Downton Abbey actor stars in new mockumentary W1A, the follow-up to Olympics comedy Twenty Twelve, which sees his character Ian Fletcher now working as a bureaucrat at the BBC.
Hugh told how while filming a sketch for the new series on location at BBC Broadcasting House, he was denied entry to the building because he didn't have the right kind of security pass.
He revealed: "In the 25 years or so that I've been coming to the BBC one thing never changes - the difficulty of getting through the front door.
The wonderful people who safeguard the portals of the BBC are as challenging in their defence of the realm as they ever were. It's quite extraordinary the palaver you have to go through to get into the building.
"We were filming in the lobby the other day, 20 of us milling around, and the chaps on the door were chuckling away watching us doing it.
"And then I tried to get back in to go and get changed and they wouldn't let me because I didn't have the right sort of pass.
"And Jeremy Clarkson was telling me he wasn't allowed in.
"People who've worked here a long time will know what I'm talking about. The bureaucracy of the machine is part of what is so loveable about it. And confusing."
W1A, co-starring Jessica Hynes, Sarah Parish and Nina Sosanya, begins on BBC Two on March 19.