Matthew Norman: Does anyone know who Ruth Kelly is?

Is she just a less irritating model from the android factory that gave us Hazel Blears?

The new Secretary of State For Doing All John Prescott's Work, to use her official title, might disapprove of the above analogy even if she agreed with the analysis, because to her the concept of hell is no metaphor but a plain fact of afterlife. Ms Kelly is famously coy about the detail of her Catholic faith, her reticence serving only to fan those flames, but her Opus Dei affiliation positions her on the far right of the theological spectrum.

So secretive is that sect that it's hard for an outsider to work out which doctrines it does and doesn't profess. However, from what we do know it is improbable that this merry band of self-flagellators would embrace the modernistic biblical revisionism that sanitises eternal damnation as a state of mind or merely the absence of God.

If Ms Kelly believes in the burning fiery furnace, that is her right. Even we atheists have beliefs that strike outsiders as preposterous (until the Sabbath Day Miracle of the Lasagne, I was convinced Spurs would ascend to the Champions League), and no one should be persecuted in the public prints for that.

Where things become tricky, of course, is in the intersect where private faith and public duty coalesce. As Education Secretary, she had some responsibility for research into the stem-cell medicine the Vatican so fears (understandably, given its potential to usurp the Creator's workload much as she has done with Mr Prescott's). As minister for equality, she must now do all she can to cement and extend the legal rights of homosexuals.

The interesting thing here isn't the intellectual dishonesty of her position. That speaks loudly and obviously enough for itself to play the part of the drunken bore at the dinner party. Clearly you can't be convinced both that the Lord abhors gay sex and that gay people deserve quasi-marital legal rights without seeing your integrity vanish into the chasm between the two positions.

Rather than strain for fancy arguments in the hope of squaring this eighth circle of ministerial hell, Ms Kelly hides behind the skirts of collective responsibility. It is a wretchedly thin argument which, by the smallest logical extension, would stretch to justifying publicly supporting genocide on the grounds that genocide is the policy of the Cabinet. To cite collective responsibility in the context of encouraging or condoning what she must regard as an abomination is nothing more than "just obeying orders" by another name.

Still, better that than constructing a piece of crazy sophistry of the type a Catholic theologian might use to explain why an all-loving, all-knowing God creates homosexuals despite foreseeing that they would grow up to commit a mortal sin by yielding to the sexual predeliction with which he so lovingly cursed them.

What is slightly more intriguing about Ms Kelly is her status as personification of the modern politician. A precociously clever child, she showed a fascination for economics at an age when most little girls her age were drooling over David Cassidy, waltzed through school and university with scholarships, worked as an economics expert for the Bank of England, and rose without much trace to reach the Cabinet at record low age for a woman of 36.

Now she has her second portfolio, and yet - apart from the religious stuff and her own advancement - still no one has the foggiest as to what she believes in. Is she a neo-Thatcherite or an interventionist, a Blairite or a Brownie, a hawk or a peacenik? She talks vaguely of a lifelong passion for social justice, but gives no important speeches fleshing out the commitment with ideas or ideals.

Is there anything there but a strong analytical mind and a grasp of economic equations? Is she a less irritating model from the android factory that gave us Hazel Blears? Or lurking behind the 15-year-old boy's face (I think of her as Perry, Kevin the Teenager's mate played by the immortal Kathy Burke) and the incongruous basso profundo voice, does there lurk a funny, lively, independent-minded person you'd love to have a friendly ruck with over a bottle of Scotch?

My experience of Ms Kelly, though brief, argues against the latter. Stood up once when reviewing a restaurant, and neurosing about having tried so little of the menu, I sidled up to the next table on the way out to ask their opinions of the food. The TV political hack Nick Robinson praised his entrecote, while Ms Kelly said her poached salmon was "very nice ... but you can't quote me on that".

Now and again I reflect on this interlude, wondering whether she might be a deadpan self-parodist. But I suspect that Ms Kelly, then a Treasury minister, was genuinely fretful of being perceived to have gone off-message by making an uncontroversial remark about a piece of fish (it must have been a Friday) to a journalist perceived as unhelpful by her political masters.

Obedience is one of the hallmarks of Opus Dei, of course, and in several other respects the cult seems to be Roman Catholicism's closest equivalent to New Labour. It loathes trade unionism while unabashedly venerating the wealthy, whose donations it needn't disguise as soft loans. Historically, it supported brutal right-wing regimes, such as those of Franco and Pinochet, as Mr Blair has done with Mr Bush. And it too appears to be a small but powerful, authoritarian and ruthlessly ambitious clique within a much broader church.

It may not use albino hitmen like the one in the forthcoming movie, and much misleading drivel may have been written about it since Dan Brown published his book. Even so, Ms Kelly's bashfulness about her involvement implies awareness that any public admission would damage her, because the beliefs it holds are in such brutal conflict with the policies of the Government she serves.

And so this paradigm of the technocratic age - a bright and doubtless well-motivated person, so much more suited to a stellar career as a Treasury mandarin - damages herself by peddling opinions that must revolt her and which expose her as every bit as hypocritical as the lecherous old goat whose job she took last week.

Although this strikes me as a far more excruciating form of self-harm than beating yourself on the back or wearing a hair shirt, Ms Kelly is deluded if she imagines herself a modern St Joan. However hot the flames, she may be sacrificing her private beliefs for her public life. To qualify as a latter day Catholic martyr, she would need to turn that equation on its head.