Someone who pontificates about subjects (especially science, especially climate change) in the pub (or, even more likely, the golf club), while having no idea what they're on about. Typically to be found drinking gin and tonic, wearing a blazer, calling people "squire", playing golf, and driving a Jaaaaaaag.
"All this global warming nonsense. The Romans grew grapes in Yorkshire! Explain that!"
"You're right, Ken. Several thousand climatologists and many petabytes of hard evidence can't stand up to a single well-informed gintellectual."