"Ladies and gentlemen", Mr Campbell or one of his young assistants proclaims, "kindly observe how, without moving my hands, I prevent Mr Ken Livingstone from becoming mayor of London." There is a flash of sparks, a puff of smoke, an acrid smell wafting over the front rows of the stalls. The lights go on and Mr Livingstone is still on the stage, grinning like a Cheshire Cat that has enjoyed an unusually good lunch. At this point Mr Campbell removes his fez and scratches his head.
In fact he seems to have kept a safe distance from the comic events of last week. Instead he, or somebody, appears to be blaming the women, Ms Margaret McDonagh of Millbank, the general secretary of the party, and Ms Sally Morgan, one of the spangled ones at No 10. Ms Morgan favoured Leninist tactics of simply eliminating Mr Livingstone at an early stage so that he could cause no more trouble to the Central Committee. Ms McDonagh, by contrast, believed - she presumably still believes - that Mr Frank Dobson could defeat Mr Livingstone in the electoral college.
Originally the nominating body had been intended to be the ordinary members in London. It soon became clear, as it had been really from the beginning, that if Mr Livingstone was allowed to stand he would beat all comers. The choice was therefore between prohibiting him from putting his name forward and changing the body that was going to be doing the selecting.
Mr Tony Blair's chums chose the latter course, duly and predictably lighting on an electoral college of one-third each for trade unions, for MPs and MEPs, and for ordinary members. This was what they had done in Wales when it turned out that, in a vote of members only, Mr Rhodri Morgan would beat No 10's nominee, Mr Alun Michael.
Another myth about New Labour, by the way, is that it is dedicated to the principle of one member, one vote. It is not. Mr Blair was elected in 1994 by a college identical to the one choosing the candidate for mayor of London: except that in 1994 trade unionists voted as individuals, as they did not in Mr Michael's election, and as they presumably will not vote either in the election for the mayoral candidate. Otherwise Mr Livingstone might still win, which would not do at all.
To choose the people to go forward sat a committee of workers, peasants and intellectuals, the most prominent of whom were Mr Clive Soley, a lugubrious Londoner, and Mr Ian McCartney, a pugnacious Glaswegian - is there any other sort? - whose father, Hugh McCartney, a Scottish parliamentary journalist, was very kind to me when I embarked on this trade many years ago. There is little doubt that the body was intended to wave Mr Livingstone through. Mr Soley and Mr McCartney claimed that, as one of them put it, he turned out to be his own worst enemy. It is not wholly clear whether his offence was to refuse to accept in advance the Labour manifesto (which, like many great works, is as yet unwritten) or, rather, to oppose the part-privatisation of the London underground.
This is yet another of those "private finance initiatives". What happens is that a public asset is handed over to a private firm (in this case Railtrack). It is then partly maintained and wholly guaranteed by public finance. After the lapse of a specified number of years, it is handed over completely to the private sector. These are schemes of such ingenuity that they could only have been thought up over the chessboard at Ford Open Prison. The paradox is that the mayor of London, whoever he or she turns out to be (for Ms Susan Kramer is there for the Liberal Democrats, as Ms Glenda Jackson still is for Labour), will have no power to jettison Mr John Prescott's misguided plans for transport in the capital. The new mayor will have few real powers of any kind. Accordingly the argument, of which we have heard a lot, that the incumbent should be someone whom Mr Blair finds congenial seems to me to be less rather than more powerful.
Anyway, Mr Livingstone is back in the contest, having on Thursday provided warranties for good behaviour. All Mr Blair has is a promise - in the argot of the People's Party, a "pledge" - that if he is rejected by the electoral college he will not stand as an independent. The moral is that, when you start devolving powers, you cannot always have either what you want now or what you had expected when you embarked on the course in the first place.
There is another example of this in the House of Lords. Mr Blair has done something no radical prime minister has done before. He has abolished the legislative functions of the hereditary peers. For this he deserves every credit. Those Conservative papers which claim that the Government has behaved vindictively or gloatingly are wrong. The change was clearly set out in the 1997 manifesto; and if Lady Jay has conducted herself with less grace than her old headmistress might reasonably have expected, neither she nor anyone else has been specially triumphalist. Indeed, the absence of whoops from the Labour benches in the Commons has been remarkable.
But the impression has somehow got about that the partially reformed Lords will henceforward behave themselves and support the Government. This is the precise opposite of what is going to happen. Until the recent end of the last session, the Government could hold over their lordships' heads the threat that, unless they did as they were told by Lady Jay and other ministers, the 92 hereditary peers would not, after all, be allowed to stay. That threat can no longer be made. The bizarrely elected lords can hang on for the time being, which will probably turn out in practice to be a long time.
In this purgatorial period they, or some of them, intend to jettison the Salisbury doctrine named after Lord Cranborne's grandfather. In its original form this was that the Lords would not oppose any measure which had been included in the governing party's manifesto. By extension it has come to mean something wider: that the Lords will not defy the will of the elected Commons.
The elected hereditaries say that these --from the Government's point of view - convenient practices should now cease. They were predicated on a House which had a majority that was both hereditary and Conservative. That House no longer exists. It has been done away with by the Government. Accordingly the Salisbury doctrine should not exist either.
The Government can still have its way through the application of the Parliament Act. It provides for a delaying power of, in practice, 13 months. In the last year of a parliament the statute cannot prevent a measure from being lost. Mr Blair can expect some reverses in the Upper House, not despite his reforms but precisely because of them. Over the House of Lords, as over the mayor of London, the unexpected sometimes happens. Cherie Blair can tell you all about that, as can Lord Archer.