“Alex,” I call to my long-suffering Catalan girlfriend, “what was number one they day you were born?”

Thud thud thud her boots resonate across out hispanically uncarpeted floor. “What, in terms of music?” she asks, her eyes narrowing.

No: in terms of fishing, I want to say in an attempt at some festive humour. But the baby’s been ill, no one is sleeping and I suspect it might go down badly. “Yes, music,” I say instead.

The eyes narrow further. “I don’t know,” she says. “Maybe that’s something for you to investigate.”

The correct answer, of course, was “I don’t know. How about you?”, to which I would have happily replied “Donna Summer’s I Feel Love”, this being the kind of question I love to be asked. But I have a theory here, so I need to press on.

“And what do you think is going to be the Christmas number one?” I ask, my agenda narrowing.

“No idea,” she says happily and wanders off.

And thus my theory is proved. You see, the Spanish love music, much like the British. We’re both, dare I say it, musical nations. But if there’s one thing the British love almost as much as music, it is a nice tidy list, one that gently ushers all the uncertainties and worries of everyday life into an easily digested, one to 100 rundown.

Combine music and lists, then, and the British are in hog heaven. And that is why the British are so obsessed with the musical charts.

Don’t believe me? OK - then ask any British people within earshot what was number one the day they were born. I’ll guess some 60% of them will be able to tell you straight off, while the rest will go and look it up. And that percentage increases when you talk to people in their 30s and 40s, setting those who have no interest in the British pop scene circa 1977 off at the risk of a serious boring. Honestly, there are whole websites and apps devoted to this number one on your birthday phenomenon.

This phenomenon extends into the current charts. OK, things in Britain aren’t quite what they once were, when weekly chart-based music show Top of The Pops regularly attracted audiences of 10m plus and having a number one record had serious cultural cachet.

But people still like to keep a vague eye on the charts in the UK. In Spain, however, I don’t think it would be going too far to say that no one gives a flying cahoot about the charts, not even those who work in the music industry, and having a number one record here is little more than an oddity. (You can apparently top the Spanish charts with something like 8,000 sales, which might have something to do with it.)

Never stronger is the UK’s love affair with the charts than at Christmas. If having a number one is a pretty big deal in Britain at the best of times, then having a number one at Christmas is like winning the lottery while scoring a date with Penélope Cruz at the clásico.

The British Christmas number one is big news, in other words: front page of the paper news; breathless chart battle news; genuine round the water cooler news. Every year - and Spaniard might find this British eccentricity a little hard to stomach - people in the UK bet millions of pounds on what song they thing is going to top the charts at Christmas.

The favourite this year, for example, is the single from the X Factor winner (announced, conveniently, just before Christmas) at 2/7, with Band Aid 30 coming in second at 9/2 with Do They Know It’s Christmas, and Iron Maiden’s The Number of the Beast coming in at third, on odds of 8/1.

The number of the, er, what now? Confused readers may be asking.

But yes, that’s hoary old heavy metal group Iron Maiden as third favourite to top the Christmas chart, with a 30-year-old song. Because, much as the Christmas number one is an immensely big deal, so to is sabotaging - for want of a better word - the festive chart.

For this - as with so many things - you can blame X Factor supremo Simon Cowell. It used to be the the British Christmas number one would throw up some real oddities, happily lurching from pop supergroup the Spice Girls in 1996/7/8 to children’s TV character Bob The Builder in 2000 and Gary Jules’ spooky cover of Mad World (from Donnie Darko) in 2003. It was, in other words, a kind of brilliant, ludicrous chaos.

And then the X Factor came along, sweeping record TV audiences before it, and from 2005 to 2008 the X Factor winner made the Christmas number one slot their own. Suddenly, competition for the sacred Christmas number one looked boring and predictable, a one-horse race that no one was even watching. And that - for the Christmas-chart-loving Brits - just wouldn’t do.

So someone took action: Jon Morter, a part-time DJ rom Chelmsford, launched a campaign to get Rage Against The Machine’s Killing in the Name to Christmas number one. And against all odds he succeed, with the song selling half a million copies in the Christmas week to beat X Factor winner Joe McElderry to the number one slot.

Ever since then, no December has been complete without a least one online campaign to beat the X factor winner to number one at Christmas. Frequently, in fact, there have been more than one, with a campaign this year dedicated to getting LFO’s bleep classic LFO to number one to mark the death of the group’s founder Mark Bell.

Why am I telling you all this? Because few things, I think, help to understand the obtuse British mentality more than these Christmas chart campaigns, which are born of the kind of spirit-of-the-underdog, perverse humour that the British have made their own.

What’s more, for any Spanish people living in the UK, this should serve as a kind of guide to what you should say when a drunk Briton corners you at the office Christmas party and asks you for your views on the Christmas number one. (“I’m backing LFO”, incidentally, is the coolest thing to say).

More than anything, though, it is this kind of celebratory festive prank that I miss about living in Britain, more so than mince pies, mistletoe and even mulled wine.

And so if anyone wants to come up with a Facebook campaign to get Slayer’s Raining Blood to number one in the Spanish charts this Christmas, you have my full backing.