How can you tell that 'Love Actually' was made in 2003? No, it isn't the Hugh Grant as a Tony Blair analogue, nor is the fact a boombox and flash cards are major plot points.

People in the 'Love Actually' universe care about what is the Christmas number one.

The idea of what makes a Christmas number one changes from person to person.

For some people, the song must be explicity Christmas-themed, such as 'Do They Know It's Christmas Time?' or 'Merry Christmas Everyone'.

For others, it can be a pop song with vaguely Christmas feel such as 'Stay Another Day' or '2 Become 1'.

On the other end of the scale, the Christmas number one can just be what was popular in the charts at the time.

'Bohemian Rhapsody' just happened to be at number one for Christmas 1975 because it's a bloody brilliant song with zero Christmas connections.

Ditto for Whitney Houston's global mega-smash 'I Will Always Love You', which had the benefit of running alongside 'The Bodyguard'.

The 80's and 90's gave us some classic Christmas number ones, with everyone from Dermot Morgan, Cliff Richard, Spice Girls and Zig and Zag claiming the number one spot.

In the United Kingdom, where the idea of a Christmas number one originated, the Spice Girls made history as the first act to have 3 conseuctive Christmas number ones since The Beatles.

Michael Jackson's 'Earth Song' claiming the Christmas number one in the UK in 1995 was seen as a sign of his untouchable status, holding off The Beatles' first release since their split (and for those keeping score at home, Boyzone were the Irish number one that year with 'Father and Son').

Last year's Christmas number one, 'Giants' by Dermot Kennedy had been in the charts for 24 weeks before rocketing to the top of the charts on the back of the song being featured in the 'Late Late Toy Show'.

The Christmas number one 20 years ago was Kate Winslet's song 'What If' from the animated version of 'A Christmas Carol' that starred Nicolas Cage (yes, really).

Sandwiched between Kate Winslet's number one was rap superstar Eminem, who claimed top spot in 2000 with 'Stan' of all songs, and 2002 with 'Lose Yourself'.

When 'Love Actually' was released in 2003, one of the weirdest Christmas number one battles was ongoing across the Irish Sea.

Glam rock band The Darkness were one of the big success stories of 2003 and were gunning for the number one slot with 'Christmas Time (Don't Let The Bells End)' until an upset happened.

Years before being used to brilliant effect in an ad for 'Gears Of War', a sombre, piano-driven cover of the Tears For Fears song 'Mad World' was used in the ending to 2001 mind-bending cult film 'Donnie Darko'.

Upon release on this side of the Atlantic, the film became an unlikely hit, quickly becoming a favourite of students.

Two years after the film sunk at the American box office, a song from the film became the Christmas number one in the United Kingdom and was the Irish Christmas number two behind 'Leave Right Now' by Will Young.

The Irish top 20 on Christmas Day 2003

In 2020, there were 0 songs specifically written to contend for the Christmas number one slot.

In their place, old classics such as 'Fairytale Of New York', 'All I Want For Christmas Is You', 'Last Christmas', and 'Rockin' Around The Christmas Tree' dominated the charts.

So why is it artists simply don't covet the Christmas number one slot anymore?

Simon Cowell may have something to do with it.

In the last 20 years, 8 Irish Christmas number ones belonged to the winners of 'The X-Factor'.

For 7 years straight, 'The X-Factor' winners had the Christmas number one single, with the streak only being broken by global mega-hit 'Uptown Funk' in 2014.

My colleague Eoghan Cannon wrote about the plight of 'The X-Factor' dominating the charts in 2018 at the expense of Irish artists.

"If you can believe it, Ireland has also had more 'X-Factor' Christmas number ones than the UK. Just let that sink in for a moment."

"However, the following years saw the 'X-Factor' dethroned from their Irish pedestal at last. We started to come to our senses, and start buying non-talent-show-related singles. Even though none of the Christmas number ones following these have been mildly Christmas related, it's been a nice 'X-Factor' cleanse."

What emerged between 2006 and 2013 and disrupted the chart landscape?

Spotify, iTunes and YouTube.

During this time there was a pushback against the Cowell monopoly of the Christmas number one slot.

Mass-downloaded songs such as Rage Against The Machine's 'Killing In The Name' (a campaign this writer credits for inspiring a love of heavy metal) and the Rubberbandits' 'Horse Outside' couldn't stop 'The X-Factor' juggernaut owing to some loopholes.

An article from The Irish Times in December 2010 broke down the situation.

"Over a busy retail weekend (remember that the Irish chart is compiled on sales from Friday to Thursday so Friday to Monday is when the bulk of sales happen), Cardle sold over 22,000 CDs and downloads of his single (that’s 43,000 units in total). Meanwhile, the Rubberbandits flogged nearly 9,000 CDs and downloads in the same period (their cumulative total is now just over 17,000). That’s over 2 Cardle sales for every Bandit purchase and it’s a gap which is unlkely to be breached by the time the final chart is compiled and published on Christmas Eve. While the Limerick act are well ahead on the downloads side of the house, they’re just not in the race when it comes to CD sales and the chart is based on a combination of both."

So while the younger generation were mass downloading Rage Against The Machine and Rubberbandits, the older demographic were buying tracks by Joe McEldery and Matt Cardle in CD form, which helped tipped the scales in their favour.

By the time 'The X Factor' ran out of ideas and stopped being culturally relevant in the mid-2010's, Spotify and YouTube streams became king, and around this time, IRMA, the company that run the Irish charts, factored streams into chart sales.

Those same campaigners who got a song about American police brutality and a horse being outside stopped participating in the process.

Since 2015, the Christmas number one has been whatever song had a grip in the charts in the run-up to Christmas, which has led to the likes of Ava Max, Lewis Capaldi, Clean Bandit and Ed Sheeran claiming the number one spot almost by default.

From the artists' end, there is little sense in releasing a brand-new Christmas song when they have to compete with the likes of Mariah Carey and The Pogues.

There have been attempts in recent years from the likes of Ariana Grande, Kelly Clarkson and Leona Lewis, but why would you listen to a new Christmas song when the classics are right there?

A "protest vote" Christmas number one campaign like Rage Against The Machine could start in the morning and may well claim the number one spot, but it would have nowhere the same impact it did in 2009.

The fact of the matter is the Christmas number one doesn't matter anymore, and audiences are largely happy to play the classics while cooking the Christmas dinner or wrapping presents.

'Love Actually' is a time capsule of 2003 in many ways, and Bill Nighy's character trying to get a Christmas number one is a perfect repersentation of just that.