Yes, yes, and the SHADO foreign secretary is responsible for Moonbase Alpha. Or was that Space 1999?
No, not at all. There are no guarantees. The composition of the Cabinet is entirely in the hands of the incoming PM, not the caucus as a whole. There are several things that could keep a particular shadow minister from becoming the minister of that department.
First, of course, the shadow minister has to get re-elected. Suppose Smith is the shadow Foreign Affairs for the opposition party, the Know-Everythings. General election is called, and the Know-Everythings sweep into power with a large majority (i.e. - they elect way more MPs than any other party). But Smith, poor fellow, doesn’t get re-elected in his own constituency, or “seat”. By constitutional convention, you have to be a member of Parliament to be named to Cabinet. So the new PM sends Smith a condolence note, and puts Jones into the Foreign Ministry.
Another thing is that the new PM has to balance a lot of internal party constituencies - must have enough from the right and left wings of his party (and every party in a parliamentary system tends to have this internal division; Maggie Thatcher derisively referred to the left wing of the Tories as the “wets”); usually have to have regional balance; must have some women; etc. What if Smith, although a good fellow, is a left-leaning guy, and the PM is concerned that he’s got too many left-leaning people already? So he might tell Smith that although he’s Cabinet material, he just didn’t make the cut this time.
And then there’s a couple of other, even more hard-ball possibilities. What if Smith was the Foreign shadow simply because they didn’t have very good people when they were in opposition? After all, you’re in opposition because you don’t have very many seats. Maybe Smith is from a safe seat (that means the people in that constituency always wear condoms and always vote for the Know-Everythings). So Smith really wasn’t very good at the job, but somebody had to do it. But now, with the big sweep, the PM has lots and lots of Know-Everything MPs to choose from, including some really smart guys and gals. Smith just doesn’t have the intellectual wherewithal to compete against them, so the PM doesn’t put him in Cabinet - makes him government house leader or something else instead.
And what if Smith was the PM’s main rival for power? Maybe, if the PM has a big enough majority, he can afford to dump Smith entirely and keep him away from the levers of power. (Actually this is pretty risky, since it might make Smith a focus for discontent within the party, and he since he’s not in Cabinet, he isn’t bound by cabinet solidarity to support government policy as firmly.)
And even if Smith gets into Cabinet, there’s no guarantee he’ll have the same ministry that he shadowed. The PM, having observed Smith in action, may say to himself, “That Smith - he was okay as Foreign shadow, but Robinson will likely do a better job. I think Smith’s talents would make him a better Home Secretary than Foreign Secretary.” And bob’s your uncle - Smith is Home Secretary.
So, all in all, it’s pretty fluid - and all at the pleasure of the PM.
The “shadow” terminology is used for the various Opposition front-benchers in Australia too.
If the members of the Cabinet remain members of Parliament, how do they divide their time between being a Cabinet Minister and representing their constituents? I would think being Foreign Secretary, Defense Secretary, and especially Prime Minister would be full time jobs in themselves. Or is a matter of they have so much power as a Cabinet member that anything they try to push through for their own constituents goes through unchallenged?
They have very good, experienced constituency secretaries who do most of that work for them.
At Westminster at least, there’s also still the expectation that even most government ministers will spend several hours a week (usually on a Saturday) holding a “surgery” with constituents. This is a session where any member of the public can walk in off the street and raise any issue of concern to them. In the case of a senior minister, the specific actions this may give rise to will normally be most quickly dealt with by them delegating them, but that’s as much a matter of them exploiting their knowledge of who to most effectively pass the request on to as anything else.
For example, Jack Straw, the Foreign Secretary, seems to hold roughly weekly surgeries back in Blackburn. Google on “Jack+Straw+surgery+Blackburn” and you’ll get relevant hits as to venues - I suspect these are frequently updated, hence I’m not linking directly. Granted, Straw is unusually identified with his constituency, but he’s not a completely exceptional case.
Blair presumably rarely does formal surgeries in Sedgefield. But his election agent John Burton is supposedly very close and supportive; I imagine the locals realise that there are such local party members with unusual influence who can fill this gap.
Actually checking, Sedgefield Labour Party has a surgery webpage with an email address for raising constituency matters. Doubt Tony sees any of those emails, but there is presumably a mechanism for others to follow them up.