INCOGNITO: Disguised as a little old lady, Queen Elizabeth II boards a passenger train at King's Cross Station in London from where she travelled to Norfolk for Christmas Picture: AP

They are probably more concerned about whether there is going to be snow on the points at Letchworth, or whether the buffet car has enough shortbread.

The chap on her left is a bit more interested, however. He takes her picture as she makes her way down Platform 11 and gets on the 10.45am from King's Cross - but then that's because he is a member of the train staff and he knows that, under the orange and white headscarf, is Queen Elizabeth.

Royalty Protection Department take note: if the queen is attempting to travel incognito, it is probably best not to opt for the old headscarf disguise. No one in Britain wears Hermes headscarves any more, except for the queen, three dowager duchesses and a woman in Knightsbridge.

It is a little known fact that when the queen travels to Norfolk for Christmas, she travels by scheduled train. It is an unashamedly royal one, however: not only does it start at King's Cross, but it takes the queen all the way to King's Lynn.

The point remains, however, that it is a regular service used by regular passengers. Although this has been her chosen mode of Christmas travel for a few years, this was the first time Buckingham Palace has allowed the press to take photographs of the event.

It will not have escaped anyone's attention that by the time the queen was seated in her first-class compartment she was looking a trifle short of festive cheer. Glum might even be the word.

Had she forgotten her senior railcard? Possibly not. For a monarch who does not carry cash, rail tickets are a fairly remote possibility. ("Yes, Mr Ticket Collector, I'm sure I had it when I left home.")

How about the company in the carriage? That rather sinister-looking man on her left, perhaps? Has he been eating salt and vinegar crisps? Talking loudly on his cellphone? Putting his feet up on the seat opposite, even? Oh. He's her protection officer. She's probably used to him. Come to think of it, he's probably got the tickets.

One explanation for her sombre expression is the one that will endear her to most of her subjects. It's the family. She's off to Sandringham, where she and the Duke of Edinburgh will be joined by members of the royal family.

Families and Christmas are a tricky combination at the best of times. The fights. The rows over who's been cheating at charades. The battles for the TV remote. Then imagine all that, with a house full of Windsors. It's a life of sacrifice, being queen.