Your starter for 10, Herr von Ribbentrop...How, one fine day, will the house of Saxe-Coburg-Gotha (UK division) come to dust? How will our royals reach the end of their line? It's a perennial question for historians, politicians, spooks. The trouble is that the answer keeps changing. After 1936 - the closest shave so far - you'd have said that Edward VIII and Mrs Simpson could do the job double-handed. There was the British establishment, flat on its back. There (an enterprising Guardian investigation now reveals) was the FBI, sure that Wallis Simpson had become a Nazi spy, prone to whisper sweet somethings in Von Ribbentrop's ear. Treachery and sex, primed to explode. Could any republican have asked for more?  Yet, even then, even in that extremity, it didn't happen. Baldwin greased the slipway, Churchill wafted the dubious duo off to the Bahamas. J Edgar Hoover declined to leak his suspicions to the press. Had Hoover, as usual, got his plots in a twist? Probably, Mrs bin Simpson. The main thing about the duke and duchess wasn't their duplicity, but their invincible stupidity. They went off to Germany together to study "low-cost housing". They had tea with Hitler in Berchtesgaden. They joked with Goering about the map in his library which somehow didn't include Austria. "Ho, ho," said the field-marshal, jowls shaking with mirth, "I needed a new map, and since Austria will soon join Germany - voluntarily of course - it seemed more economical to anticipate the event." And the duchess, in her own memoirs, wrote all of this rancid stuff down.  Never underestimate the dogged strength of royal stability pacts. They paper over every imbecility. They distract and move on. They give the institution of monarchy a resilience which stretches far beyond rationality.  No, the Windsors will not easily go this way. But, since all dynasties depart at some time, the question remains: how will they go? Here the winds of changing opinion blow.  There will not, as constitutional reformers such as Charter 88 once fondly believed, come a decisive moment when a government of the left decides to cleanse our body politic of its flummeries. The case for cleaning away the dung of deference is as strong as it ever was; but the force is not with it. You can publish pamphlets till kingdom come - but, in practice, the kingdom won't be moved.  Nor, frankly, will personality disorders of the kind which surrounded the death of Diana bring the monarchy down. We've seen what happens in the wake of such PR disasters: a new team of spin doctors is recruited, a new PR pitch smoothly developed. There's no natural close to such a recycling process. Pay the right man the right money and you can survive indefinitely.  In fact, it now emerges, the true threat to continuance lies elsewhere - in the vociferous advice of those who claim to be the royal family's greatest friends and defenders. Take, for instance, the Daily Mail, puffed with triumphalism after the Queen Mother's funeral and a golden party of a jubilee - and cheerfully duffing up this paper for trying to rain on such parades. Well, fair enough ... but then the Mail leads the charge against Princess Pushy and her 69-a-week Kensington Palace apartment. Pushy and Bushy, a new pair of royals on the make to revile. It's a scandal. MPs begin sounding off, the pressure grows.   This isn't a Guardian campaign, though. It's a Mail campaign. The damage, however, could hardly be greater. Love and affection for HM, as commodiously chronicled at the start of June, turns swiftly to carping about the greed and arrogance of her family. She who was strong after 50 years is made to seem weak again. But what is the charge here, what's the offence? Of family looking after family, of more fortunate and moneyed Windsors taking care of the weaker brothers and sisters? It seems a slightly bizarre crusade from the ultimate newspaper of self-help and family values.  The thesis, expounded a few days ago when the keeper of the privy purse - formerly of KPMG and not, praise heaven, Arthur Andersen - published his household accounts, is that you can keep the palace show on the road if you deliver good accounting value. Wine bills down from 135,000 to 97,000 year on year. (Out with the fine Bordeaux, in with South African merlot.) Helicopters down from 2m to 1.9m. Crockery and cutlery down from 16,000 to 11,000 - but stationery up from 14,000 to 22,000. And so on, in close detail. What you lose on the fire insurance premiums you try to make up on flowers, photocopying and second-class postage. Now, if they could only stop washing the sheets so often!  The headline calculation from this exercise - the figure that puts the squeeze on Pushy's 69 - is that keeping our royals in the manner accustomed costs every Joe Citizen 58p a year. Good value as long as you can keep selling surplus carriages and keep staff wages down by paying them in minor gongs rather than money.  But step back for a second and ask that bigger question again. If this is the kind of majesty we want, why not crown the comptroller and auditor general instead? The jubilee wasn't a success because we counted every sparkler; it was a success because we spent loads and loads of cash. Our monarchs don't travel EasyJet; they cost nearly 4m a year buzzing around.  Royal household wisdom. The Windsors are conspicuous consumers. That is their way and our way with them. Holding their contract cleaning bills up to the light won't save them - to the contrary. Down the pan and round the bend with Tesco's own label Harpic substitute? Salvation isn't value for money. Salvation is living and playing rich, salvation is looking down, not adding up - as even Mrs Simpson was bright enough the understand.