There’s a wired-shut skylight, and the wind howls and gibbers overhead: occasionally there’s a sound like gravel on concrete as an errant gust flings a cupful of freezing cold water at the glass, followed by a hollow booming noise from the chimney. The chimney is indeed warm, but it’s cooling fast: I guess they’ve shut down the incinerator over the holiday period. It’s just past eleven at night, and there’s no way in hell I’m going to be able to sleep while the storm is blowing.

When the holiday falls on a weekend day (as Boxing Day does this year) everyone gets a day off in lieu at the beginning of the following week except the Night Duty Officer, who is in it for up to four days at triple pay-as long as he doesn’t go mad with boredom first.

I’ve been on duty for six hours and I’ve already caught up on my work email-at least, I’ve replied to everything that needs replying to, and am well into ignoring all the Powerpoints that need ignoring-and gotten bored with gaming. The TV’s on in the background, but it’s the same-old family-friendly fare. I don’t want to start on the two fat novels I’ve stockpiled for the weekend too early, so there’s only one thing to do. I abandon my cup of tea, pick up my torch, iPhone and warrant card, and tip-toe forth to poke my nose where it doesn’t belong.

’Twas the night before Christmas, the office was closed,

The transom was shut, the staff home in repose;

The stockings were hung by the chimney with care,

But St. Nicholas won’t be coming because this is a Designated National Security Site within the meaning of Para 4.12 of Section 3 of the Official Secrets Act (Amended) and unauthorised intrusion on such a site is an arrestable offense…

Had enough of my poetry yet? That’s why they pay me to fight demons instead.

One of the perks of being Night Duty Officer is that I can poke my nose anywhere I like-after all, I’m responsible for the security of the building.