A DOCUMENTARY called The Beatles: Get Back is taking the world by storm just now and it got me thinking.

Although there are several - maybe even hundreds - of memorable moments throughout the three-part series, what stood out most to me was the studio sessions in episode one.

In amongst the day-to-day jams, the tea, the toast, the riffs and the rabble, it seems obvious that Paul McCartney was their true driving force. But, more than that, it showed that even arguably the most influential band in history - then 12 albums deep, remember - still needed to have one.

We watch on as one of the most creative and individually-talented bands of all time struggle to produce some days and realise one of them more than the others feels the responsibility and embraces the weight of what's at stake enough to make sure the rest remember what they're there to do and why it's so important.

So I've decided Callum McGregor is Celtic's Paul McCartney.

That's probably not a combination of words I, or probably anyone, thought I'd see written down. But there it is.

Who the other three are on any given day is, I suppose, up to you. But to me McGregor is Celtic's McCartney. That’s just the way it is.

In this context, Sunday’s win over Dundee United is not likely to be considered a truly brilliant moment in time. It's not like the scene of McCartney plucking the guts of the song Get Back out of thin air while Ringo Starr and George Harrison sit yawning and smoking as they wait for John Lennon to arrive.

Neither is it like the pivotal (and altogether more sinister) scene when the producers have hidden recording equipment under a table to catch what football parlance dictates we must call 'crisis talks' between McCartney and Lennon over Harrison's threat to quit.

How could it be when it was all so positive and McGregor had Tom Rogic creating chaos in and around the United midfield and defence? Or Kyogo Furuhashi dragging the centre-backs every which way? Or David Turnbull pulling off pirouettes that would make Darcey Bussell proud?

Nah, with all that going on it was never a 'crisis talks' kind of afternoon.

It's probably more akin to some of those other days in the documentary. The ones when the four sit around jamming, trying to find their creative spark and generally going through the process of hitting their groove. It's those kinds of days that are required as much as the ones that produce instant classics.

And it's on those such days you need someone in the thick of the action making sure the routine not only stays routine but actually becomes enjoyable.

Because while the result at Tannadice could definitely be called routine, the performance was anything but humdrum.

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The hosts had the joint-third stingiest defence in the division when Celtic rocked up on Sunday lunchtime. They'd conceded just four at home all season - by the end of the game that had almost doubled and probably should have.

With Jota and Anthony Ralston injured, the starting line-up contained Mikey Johnston and Greg Taylor. The latter made his return from a lengthy injury and has already posted a reminder of the benefit of having a natural lefty playing in that role in terms of variation and unpredictability in attack.

The former, well, it would be hard to replicate what Jota brings to the party but he made himself a problem for United all afternoon even if an end product was lacking.

As for the rest - there were positive displays from Cameron Carter-Vickers and Carl Starfelt, reunited for the first time since Starfelt's injury against Livingston in October, and the aforementioned Rogic flexed his considerable creative muscles in his 68-minute run-out.

But at the centre of it all was McGregor. Ostensibly playing as the deepest midfielder - until Nir Bitton's arrival anyway - the captain not only kept possession in his usual manner but played several incisive passes and notched an assist for Turnbull's goal.

After Bitton's introduction he moved further forward and popped up on both bylines after marching into the Terrors box. It felt like he was everywhere.

Not only that but when United did put together some semblance of attacking play, it was McGregor intercepting the danger on more than one occasion too.

He is never one to pontificate - and of course there is an argument he's not even the most talented player in the team, strictly speaking - but when there was even a sniff that United might disrupt the groove Celtic had found, McGregor was the one telling and showing the rest of the band how to push through it.

In Get Back you come away with the impression McCartney was that person for the Beatles in the studio, certainly at that time. For Celtic, on the pitch, that's McGregor. He is the driving force.

Sure, Postecoglou is on the sidelines and can make his feelings heard most of the time but generally it's up to the players to perform over the course of 90 minutes.

Or, as McCartney says about the absence of late manager Brian Epstein during one of his attempts to inspire his bandmates to maintain their own impeccable standards: "There's no-one there to say 'do it'. Daddy's gone away now and we're on our own at the holiday camp. We either go home or we do it."

Celtic do it, and a large part of the reason why is McGregor.

More days like the one they just had at Tannadice and they'll get back to where they once belonged soon enough.