Here's a question for the Catholics among you: Are you married?

Here's another question: Are you sure?

The reason I ask is that neither news reporters nor religion correspondents appear to understand Church teaching on Matrimony. I, on the other hand, always take care to cover my tracts and have lately re-read the relevant sections of Dr. Ludwig Ott's definitive and fascinating "Fundamentals of Catholic Dogma" in order to make sure that I am right, again.

The question of what constitutes a valid Catholic marriage has popped up in all sorts of places in the wake last month's wedding of the portly fraud of Downing Street to the upscale whizz of the wallpaper world, Carrie Symonds.

Boris "Lies R Us" Johnson had been married twice before his co-starring role in the gaudy mockery at Westminster Cathedral.

As a zillion sudden experts in theology have explained in broadsheet journals since, Johnson had previously been married twice, to Allegra Mostyn-Owen (1987) and Marina Wheeler (1993). So, they argued, a question mark must loom over the validity of his fusion with Ms. Symonds.

This was to miss the point.

Catholic marriages have been annulled on a regular basis for at least a thousand years. The conditions for annulment have always been the same, money or rank. You show you got the assets, the annulment is in the post. A more respectable rationale for rending asunder what the putative god has put together can always be found later in the bible or Christian tradition or in anything which meets the needs of a monied person at any particular moment.

All eternal dogmata exist in a constant state of adaptation to changing material circumstances.

Take the Vatican's explanation of the fact that more than half the annulments granted by the Church in recent years relate to "marriages" made in the United States. The argument goes thus: that American culture demands maximum self-fulfillment in all aspects of life and that this must include what can reasonably be expected of a marriage. If you find yourself unfulfilled, then, you can plead that this is not what you signed up for, and feel free to walk out and slam the door behind you.

Consider the Kennedys. Massachusetts Senator Edward had his marriage to Joan annulled in 1990 after he formally admitted that he hadn't been honest when he'd vowed to be be faithful. Head hadn't been in the right place. Ceremony didn't count.

A few years later, Ed's nephew Joe had his marriage to Sheila Rauch (pronounced "ouch") annulled on the ground that he had been mentally unfit at the time of the ceremony to the extent that his vows could not reasonably be regarded as genuine.

Or, to put it all another way, the Kennedys were Catholic royalty and normal rules didn't apply.

(Joe's annulment had been granted by the Boston archdiocese. Outraged, Rauch-Kennedy, an Episcopalian, appealed the annulment to Rome, seemingly just to make sure he wasn't let away with it – as excellent a reason as anybody could ask for. Some Episcopalians obviously take Catholic sacraments more seriously than the archbishop of Boston.)

Left out of almost all these pontifications has been the question of consummation. In Catholic theology, the essential purpose of marriage is to bring children into the world. The hungover ceremony at the altar, the scrawly signing of the register, the booze-filled bacchanalia in the hotel at the top of the town, none of these or all together validates a marriage. No. The key condition for validation is consummation.

The Church has had to define what's involved in consummation. A quick grope on the back seat of the bus to Borderland wouldn't suffice. Or leading with the tongue in a snog situation. For avoidance of doubt, the procedure has to be spelt out. As indeed it is, and in Latin. And has become my favourite passage of other-worldly wisdom.

Erectio, introductio, penetratio, ejaculatio. That's what's required. And in that order.

A sequence of erectio, introductio, ejaculatio would be non-validating. Likewise, and even more obviously, erectio, penetratio, ejaculatio, without so much as an introductio. This rules out the traditional Irish male injunction to, "Brace yourself, Brigid!"

The bottom line is that validation of a Catholic marriage requires foreplay. You'd think that would be taught in the schools.

Which brings us back to my opening questions: Are you married? Are you sure?

(Incidentally, the last British prime minister to get hitched in office after a previous marriage was the notorious philanderer and thief Augustus Henry Fitzroy, third Duke of Grafton [1735-1811], after whom Grafton Street is named.)

The only good reason for having mentioned Carrie Symonds is that she provides a hook to hang a Dory Previn lyric on.

"Shall I make you in the morning /A cup of instant coffee/I will sweeten it with honey and with cream / When you sleep do you dream / You can read the early paper / And I can watch you while you shave / Oh god, the mirror's cracked / When you leave will you come back / You don't have to answer that at all / The bathroom door is just across the hall / You'll find an extra towel on the rack / On the paisley-patterned papered wall / There's a comb on the shelf / I papered that wall myself / Would you care to stay 'til sunrise / It's completely your decision."

I try not to go a week without singing or saying a verse from Dory Previn.