A diminutive, slightly stooped old woman gets on to a train, unnoticed by most of her fellow travellers. 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 10.45 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, it’s the Queen.

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 this country wears Hermès headscarves any more, except for the Queen, three dowager duchesses and a woman in Knightsbridge.

It is a relatively little known fact that when the Queen travels to Norfolk for her Christmas break, 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 (by which time, if she were human, she might be wondering, wouldn’t Queen’s Cross be a rather good name for a station? Or Queen’s Lynn? Or Queen’s anything?).

The point remains, however, that it is a regular service used by regular passengers. No helicopters for her, or chartered flights. Although this has been her chosen mode of Christmas travel for a few years now, this was the first year that Buckingham Palace has allowed the press to take a photographic record of the event: perhaps the Queen is planning to send a copy of the picture to the Prince of Wales and the Duke of York.

It will not have escaped even the most casual of observers’ attention that by the time that 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 this morning. Let me check my handbag once more. It’s in here somewhere.”) 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 mobile phone? 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.

(Should anyone ask, the 95-minute journey costs £44.40 for a first-class ticket, and £27.70 for a standard seat. When things get really tight, there is a £16.70 annual saving that can be made without trying.) The one remaining explanation for her sombre expression is one that will endear her to most of her subjects. It’s the family. She is off to Sandringham, where she and the Duke of Edinburgh will be joined by several 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 television remote. Then imagine all that, with a house full of Windsors. It’s a life of sacrifice, being Queen.

Royal progress by ordinary means

•After attending the play War Horse this month, Prince William and his girlfriend Kate Middleton jumped into a cab. After a five-minute walk through Central London accompanied by two protection officers, they gave a taxi driver in High Holborn a great story to tell future passengers

•In 1998 the Prince of Wales and Prince Harry forsook the fleet of royal planes, trains and private helicopters, and took the Eurostar to Lille to see England play Colombia in the World Cup in Lens, northern France

•In 2006 the Princess Royal surprised passengers on the 10.17 from Paddington to Kemble by arriving in first class with her entourage

•Queen Victoria was the first reigning sovereign to make a train journey — from Slough to Paddington, on June 13, 1842

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