On December 7, 1973, Slade released "Merry Xmas Everybody."

To say the single was the capper of a successful year is a vast understatement. After all, the flamboyant glam-pop rockers had already landed two No. 1 singles, "Cum on Feel the Noize" and "Skweeze Me Pleeze Me," earlier in 1973. Appropriately, "Merry Xmas Everybody" is also an exuberant song that starts off with fantastical visions of a corker of a holiday ("It's the time when every Santa has a ball / Does he ride a red-nosed reindeer? / Does a turn upon his sleigh? / Do the fairies keep him sober for a day?") and leads into families having a blast and pondering all the festive fun they'll have.

Musically, the song isn't necessarily the most holiday-reminiscent, which is partly why it works so well: The harmony-heavy chorus makes it suitable for hoisting a pint in the pub or at Christmas dinner, and its chugging tempo and jagged guitars are both urgent and laissez-faire.

As the story goes, the mother-in-law of Slade bassist/violinist/songwriter Jimmy Lea, who co-wrote the song and worked up the verse melody and chorus words, is responsible for the song's existence. "She said to me, 'Why don't you write a Christmas song, Jim?' I got a bit annoyed," he told The Guardian in 2011. "I was young and full of testosterone, and, 'Don't tell me what to do, we're top of the tree.'"

Still, others in Slade's camp (including producer Chas Chandler) also wanted the band to craft a holiday tune. Luckily, Lea had an ace up his sleeve: Back in 1967, vocalist Noddy Holder had written a song with a Sgt. Pepper's Lonely Hearts Club Band-reminiscent chorus. That part popped in Lea's head one day and sparked more inspiration. "I never forgot that chorus, and I was in the shower in America somewhere thinking - Bob Dylan, Bob Dylan - and suddenly out came, 'Are you hanging up the stocking on the wall?' and I thought, 'That'll go with that chorus Nod did in '67,'" he once told Record Mirror.

After also conjuring the 'So here it is, Merry Christmas' part, Lea approached Holder with his raw material. The vocalist hunkered down at his childhood home in Walsall for festive inspiration. "I wanted to make it reflect a British family Christmas," Holder told The Daily Mail in 2007. "Economically, the country was up the creek. The miners had been on strike, along with the grave-diggers, the bakers and almost everybody else. I think people wanted something to cheer them up—and so did I. That's why I came up with the line 'Look to the future now / It's only just begun.'"

A few hours later, the framework of the song had emerged. "Once I got the line, 'Does your granny always tell you that the old ones are the best?' I knew I'd got a right cracker on my hands," Holder added. "It says it all. We've all heard someone's granny say it - usually after a couple of sherries when her bloomers are starting to show and she's up dancing."

The band headed to New York City and recorded it at the Record Plant, a studio with good mojo. "John Lennon was doing his Mind Games album, and the volume knob had got 'John' on it, so we had that taken off and a new knob with 'Slade' put on," Lea recalled to The Guardian. "It was very humid and to do our vocals we needed an echoey place, so we used the lobby of the record plant."

The sales demand was staggering, according to the band's January/February 1974 newsletter. The single was certified Silver (for sales of 250,000 copies) on pre-orders alone—"the first time a single has done this since the days of the Beatles," the missive touted—and sold 500,000 copies the first week of release. "Such was the demand for their latest single that Polydor had to make special arrangements to have 250,000 discs sent from Los Angeles, as well as 30,000 copies a day they were receiving from Germany," the newsletter added triumphantly, while noting sales were at one million and counting.

Naturally, "Merry Xmas Everybody" entered the U.K. singles charts at No. 1. For the record, the song also beat out another future holiday classic, Wizzard's "I Wish It Could Be Christmas Everyday," on the way to the top. "Merry Xmas Everybody" also stayed atop the charts through January 1974.

The song regularly re-enters the U.K. singles chart each holiday season - in 2017, it even peaked at an impressive No. 16 - and has been covered by dozens of artists, including R.E.M., the Cure, Oasis, and Cheap Trick. Unsurprisingly, in 2015, The Daily Mail estimated "Merry Xmas Everybody" generates an eye-popping 500,000 pounds (roughly $636,549.50) in royalties every year.

"It looks as if it's never going to go away," Lea told The Guardian. "It could be here in 200 years' time. I think it's because of the way the melody lilts around and it's got a happy-sad feel. It sounds nostalgic."