At 85 and on one of the coldest days of the winter, there was no likelihood of the Queen peering out the window at the heavy snowfall and saying to her husband, not long out of hospital after a heart scare: "I think we'll give church a miss this morning."

Instead, in warm woollen coat and hat and leather boots out she went as usual, the Duke of Edinburgh at her side.

And after the service, there was no hurrying back to the fireside, to stroke the warm rump of a favourite Corgi. Instead, the usual form prevailed, stopping in the chilly Sandringham air to make small-talk with wellwishers including a boy who brought along a bag of Werther's Originals for Philip.

It's a decent stab at a gift for an old man, because the truth is that despite a lifetime in the public eye there are few hard facts about the likes and dislikes of this extraordinary couple, let alone an insight into their enduring love affair. To mark her Diamond Jubilee, a raft of new royal tomes all promise revelations, such as the secrets of HM's handbag - a lipstick, a £10 note and a tissue. But who really knows? The only certainties about this hugely popular monarch come down to the same theme - constancy, endurance, duty.

Which is also why she broke with her usual routine of spending yesterday privately to smile through several engagements.

Because February 6 is always a day of mixed emotions for the Queen - the 60th anniversary of her ascension to the throne but also the day on which her father died. We really do cut her very little slack. She's the Queen, this is the Diamond Jubilee so on with the celebrations.

Amid all the pomp and circumstance, though, a diminutive grey-haired woman, 20 years past pension age, works through a long ago but abiding grief to keep the royal show on the road. Makes you think.