In the UK, "Middle Class" is more of a mindset than an economic class (although economic class is definitely a part of it).

You can think of it more as the US middle-upper-class.

This musical number from the UK comedy "Mongrels" more-or-less nails the mindset:

https://www.youtube.com/watch?v=_Yr4yEguWrw

Yeah I know the difference between economic and social class. I'm saying that's the wrong social class for the Economist.

I'm British, have read the Economist in the past and a friend of mine interned there. I think "middle class" is bang on to describe their audience, which ranges from aspirational students to working professionals who want a quick news summary with some wit. Not many builders (working), dukes (upper) or Oxford faculty (upper middle) would be caught reading it. It's definitely seen as middlebrow fodder for undergraduates.

One of the catchy Economist adverts claims "99% of the 1% are subscribers". I get to interact now and then with this demographic and conversations often use a recent article in The Economist as a starting point. It may be middle class in the country it is published, but it has found elite clientele around the world.

What is the more high brow alternative?

Depends what topic you're going for but the guardian or ft, tatler, London or new York review of books, times literary supplement etc would be found in eg a London club library. Economist too, it's a light but fun read.

Are you really saying The Guardian is higher-brow than The Economist? As a regular reader of both I would never have guessed it. (I'm not British, if it matters.)

It's probably the highest brow of the mainstream (ie, non FT) newspapers. It's seen as less try hard and pseudointellectual than the Economist i think.

The Guardian is probably the most often quoted publication in Private Eye's "Pseuds Corner", a regular selection of unintentionally amusing psuedo-intellectual writing.

Oh no doubt, I'm just talking about general perception. The Economist hides its pseudiness better, behind the simple writing style (which I enjoy).

My perhaps incorrect impression has been that middle class means something a bit different in a country with royalty.

Back when they were still moderately important publications, Time and Newsweek were probably similar although more US-centric and mainstream. But similar in that they tended to draw from the Ivies and other establishment schools. Likely significant overlap with the Times and the Post.