It was a fantastic tv show, written by insiders. One of the few shows about politics where you can actually learn something. And I have been told real stories from french ministries that mirror exactly what the show depicts in british ministries.
Ha-Ha-Only-Serious response: I've actually been told that ministers are explicitly selected to portfolios that they know nothing about so that they an be an impartial filter for the people working in that area. You don't choose an Information Minister because they're an IT guru, you choose them because they have no knowledge of the subject (and hence no personal preference or bias) and they will just go with whatever the actual experts working 'below' them say.
My understanding is that in a parliamentary system, ministers are selected from parliament. (The US equivalent would be something like making a rule where every cabinet secretary had to also be an elected member of the House of Representatives.) So the expert would have to first run for parliament and be elected.
In the parliamentary system here, only the Prime Minister is selected from parliament. The other ministers are selected by the PM, and don't have to be (and usually aren't) members of parliament.
In all parliamentary systems I know (Spain, France, Morocco) ministers do not have to be selected from the parliament. Parliament is legislative while ministers are executive.
> - Then why not directly make one of those experts actually the Minister?
If you watch Yes, Minister (and Yes, Prime Minister), the show's thesis is that the system is mostly set up so that the civil service can run things regardless of whatever policies the politicians are trying to implement.
To take the blame, mostly, as far as the show is concerned. Hacker even says it in one episode, I think the one about the civil service pay rise (or maybe the one about civil service honors). Going from memory:
Sir Humphrey: Civil servants are paid but a modest wage.
Hacker: Modest? You make more than me. Compared to who?
Sir Humphrey: Comparable positions in industry.
Hacker: In industry, when you do something wrong, you get the boot. In civil service, when you do something wrong, I get the boot.
What I meant is that if there's no consensus and the third, the fourth, the fifth... also either have a different proposition/idea or are divided somewhat equally into both sides.
Sir Humphrey: Well, what is he interested in? Does he watch television?
Jim Hacker: He hasn't even got a set.
Sir Humphrey: Fine, make him a Governor of the BBC."
-- Yes, Prime Minister