British Prime Ministers are either vicars or bookies: quote origin?

Apparently, the phrase is from an article in The Spectator (paywalled), 6 April 1956, p. 8, by Charles Curran. In an article titled "Liberty, Equality, and Mr. Gaitskell", the subsection titled "The Professors Take Over" starts with

To become a successful political leader in Great Britain you must be either a bishop or a bookmaker. The bishops are a distinguished lot — from Gladstone, the greatest of them all, to Balfour, Asquith, Cripps, Attlee, Eden, Butler. So are bookmakers — Disraeli, Lloyd George, Churchill, Mr. Bevan.

The tragedy of British Socialism is that its leadership has now fallen into the hands of men who are neither bishops nor bookmakers but professors; men with neither fervour nor gusto, who shrink both from the cakes and from the ale.

The lead-in to this from the main article ("Liberty, Equality, and Mr. Gaitskell") is

Skilfully coated, a bolus of self-contradictory absurdities can be fed with ease to a large part of the mass electorate. The entire history of British Socialism, from the 1890s to 1945, demonstrates this truth. Egalitarianism is no more discreditable, in propaganda terms, than was 'Stand up to Hitler and abolish the Army' or its post-war equivalents 'Cut the taxes and restore the subsidies.'

But how many votes are there likely to be in egalitarianism? To answer that question, let us look first at the people who are playing with it.

Curran's bon mot is then paraphrased in an essay by David Marquand, "Sir Stafford Cripps: The dollar crisis and devaluation", included in a 1963 volume titled The Age of Austerity (last paragraph, p. 159):

As Mr. Charles Curran once remarked, the British people like their leaders to resemble either bishops or bookies.

To comfort him I developed on the spur of the moment a theory, often propounded subsequently - that to succeed pre-eminently in English public life it is necessary to conform either to the popular image of a bookie or of a clergyman; Churchill being a perfect example of the former, Halifax of the latter. -- p45, Malcolm Muggeridge, The Infernal Grove, 1973

There might still be an earlier one, or he may be repeating himself from earlier journalism, or both.

The tip from @peterG in the comments led me down the right rabbit hole. The "bishops" version does seem much more popular than "vicars".