In the classic episode of "Yes Prime Minister" in which the hapless Jim Hacker has to appoint a bishop, his long suffering private secretary explains the process to him: "It's like any choice the Civil Service offers, Prime Minister - it's a conjuring trick. You always take the card they want you to take."
"Suppose I don't?"
"Oh you will…."
Probably before the summer, a new Clerk of the House of Commons will be chosen, and, while previous appointments may have followed something a bit like the process above, this time it is different.
An advert will appear in suitable newspapers in the next few weeks, interviews will follow in June and the hope is that a successor will be anointed before the House rises for the summer.
But all is not harmonious.
The key to the behind-the-scenes arguments now raging is that the Clerks are the "High Priests" of the Commons. They advise the Speaker on issues of procedure and the constitution, which is a highly specialised role for which the top clerks have trained for decades.
Some think they're over specialised, so adapted to their Westminster environment that it can sometimes be difficult to see where that environment ends, and they begin. And it is worth adding that the job of Clerk does not end with the "priestly" functions; they're also the Chief Executive of a sprawling organisation, which covers everything from security to catering to the keeping of official records, the accommodation of MPs and the Commons' increasingly important digital footprint.
One bone of contention is who chooses the next Clerk?
Formally speaking, it is a Royal appointment, made by the Sovereign on the advice of the prime minister, but you have to strip back a couple of layers. Because this is a House matter, the prime minister takes advice from the Commons before making a recommendation to the Queen. So while Downing Street would doubtless perform due diligence, the actual name would emerge from the bowels of the Commons system.
When the current Clerk, Sir Robert Rogers was appointed, he was the choice of an interviewing panel which included the Leader and Shadow Leader of the House, the Chair of the Liaison Committee and representatives from the Commons administrative arm, the House of Commons Commission, under the chairmanship of the Speaker.
And, as with any major public appointment, there was also an independent person from outside the organisation.
That was a big departure from the hallowed method under which two names "emerged" from the internal hierarchy and were offered to the Speaker of the day. So there is a recent precedent for a formal appointment process but there are no rules set in stone.
And here we trip across the Commons oddity that the powers of the Speaker, are sweeping, but almost never actually used.
Already there is some to-ing and fro-ing over the people who might serve as the "independent person" and more particularly over the job description.
I'm told - although his camp will not confirm this - that Speaker Bercow has been "bigging up" the executive side of the job and downplaying the procedural advice side, so that the draft now calls for "awareness" of parliamentary procedure, where the original version required "detailed knowledge."
The point about this is that it allows the recruiters to fish in a much deeper pool. "Detailed knowledge" means that possible successors would have to be drawn from the ranks of the Westminster clerks, plus, perhaps, a few possible candidates from other Commonwealth parliaments and the Scottish Parliament and the Welsh and Northern Ireland assemblies.
"Awareness of" would permit outside executives, perhaps senior civil servants and other figures to be considered.
Is this a good idea?
The Clerk of the Commons is a pretty singular role and its occupant has to be deeply attuned to the mood of Westminster and the eternal tensions between the government and the legislature.
To be sure MPs sometimes find clerkly conservatism frustrating. It can be easy to dismiss them as a kind of bronze-age priest class, poring over sacred texts and muttering incantations. But they see themselves as the institutional memory of the House protecting its rights and procedures from government and sometimes from MPs themselves.
On the other side of the argument there are plenty of people who move from company to company and institution to institution, and adapt perfectly well, and Mr Speaker's camp regard it as absurd, in the 21st century, that an appointment of such importance should not be made after considering the widest possible range of candidates.
The muscle-flexing over the Clerk could set a precedent for a couple of other vacancies at the top of the Commons apparatus, for Librarian of the House (providing impartial research to MPs - anyone researching any public policy issue would be well advised to go on line and look at the library research briefs that department publishes; they are impeccable) and for the new post managing the online presence of the House.
Although it's worth remembering that the Librarian (Director-General of Information Services, if we're being picky), John Pullinger, was an external appointment and the walls of Westminster did not come tumbling down.
All this may have a familiar ring to Whitehall watchers, who've listened to ministers grumbling about the permanent officials that surround them, and hankering for a more open appointments process which would bring in some fresh air.
At least one strand of this argument seems to be Mr Speaker's frustration that his push to reform the workings of the Commons has had to proceed in baby steps. This is not to say that Sir Robert has been a force of conservatism; on the contrary he is a Commons reformer and has helped devise many of the improvements to procedure which have been implemented in the 2010 Parliament.
But he became a clerk a full quarter century before the current Speaker first became an MP, and may have a different perspective on some issues. It is rumoured that the two have had some blazing rows.
Hence Mr Speaker's reportedly lively interest in the appointments process - but he is encountering resistance, and murmurs of concern are audible in quiet corners of Westminster.
One reason for this is that an activist Speaker is almost a contradiction in terms.
Speakers are supposed to preside like constitutional monarchs - only employing reserve powers in times of extreme crisis.
But John Bercow was elected to the Chair on a pledge to promote reform, and he has done so. His decision allowing an extra amendment to the Queen's Speech in 2013 may be the most important ruling by a Speaker for decades.
He is less a constitutional monarch than a Commons Napoleon.
Napoleon, of course, was eventually forced into abdication and exile.
At the moment, John Bercow is pledged to serve until the middle of the next parliament (usually considered the best moment for MPs to choose a new Speaker) but the chatter about a coup against him is rising again. Some Tory MPs dislike his interventions at Prime Minister's Questions and others resent his put-downs to errant ministers. The appointment of a new Clerk could provide a new and nagging irritant, if others within the Commons' maddeningly diffuse power structure are not pacified.
And Mr Speaker's enemies know they would have to strike before the end of this Parliament, because no incoming government would want its first act, and it would literally have to be its first parliamentary act, to be to sack the Ref.