The man who gave voice to worldwide hits including Squeeze's Tempted and Mike & the Mechanics' The Living Years has been so involved in touring and recording this past year that he hadn't been aware, until the Herald prodded him, that the fortieth anniversary of the song that gave him his first toe in the door of the music business, How Long, is coming up in 2014.
"I genuinely hadn't realised that, but you're right," he says down the line from his recording studio.
"Those were very exciting times because we'd formed Ace to have some fun playing some rock'n' roll in pubs and we were the last of the pub rock bands, who were in vogue at that time, to get a record deal.
"Then suddenly we had a hit on both sides of the Atlantic. Well, I say suddenly. It wasn't that sudden."
Indeed, How Long was a textbook slow burner. Written on the back of a bus ticket on the way to Carrack's future in-laws, where he got his one decent meal of the week in those days, the song told the story of an actual situation.
Another band had been trying to poach Ace's bass player, Terry Comer, but Ace prevailed, Comer stayed, the song went into the set they played on the London pub circuit and it was one of the sales points, along with Carrack's distinctively soulful voice, that got them signed to Anchor Records, home also to Scottish funksters Cado Belle.
"It's funny because that song didn't turn out anything like how I imagined it was going to sound," says Carrack.
"I was thinking of the Four Tops or Northern soul but we were a laid-back bunch in Ace and we kind of got caught up in the west coast American sound that was all the rage then.
"Which, looking back, possibly helped us in the States. Eventually. Because it crept and crept its way up the American top 100 until, depending on the chart you believe, it reached the top. Unbelievable. Your first single and it's a huge success. How do you follow that? Well, we didn't - but that's life."
How Long went on to enjoy a life of its own. Imminent Celtic Connections visitor Bobby Womack recorded it, much to Carrack's pleasure, as did Rod Stewart. There were even high profile country, disco and reggae versions and it's still Carrack's most played song on the radio.
Meanwhile, through the legendary London music business figure Jake Riviera, Carrack was invited to replace Jools Holland in Squeeze, sang Tempted at the suggestion of Elvis Costello, who was producing the song's parent album, East Side Story, then moved on to Mike & the Mechanics, Mike Rutherford's highly successful sideline away from Genesis.
"I've never gone after jobs like those," says Carrack. "With Squeeze, I know they were stuck for a keyboard player because they'd tried loads of different guys and I wasn't exactly new wave - I had a beard, which I thought would have ruled me out - but they were due to record their next album the following week and I went in and it turned out quite well. Mind you, if I'd been Glen Tilbrook and Elvis Costello had given someone else my song to sing, I'd have been really miffed."
The invitations have kept on coming. As we spoke Carrack had just returned from playing concerts in Germany with the SWR Big Band, singing jazz standards, an annual occurrence since he recorded a Christmas album with one of Germany's top radio orchestras in 2006. And one of the reasons why 2013 was so busy was Carrack taking a call from Eric Clapton, with whom he's worked with occasionally before, asking him to join his world tour in Los Angeles the day after Carrack finished touring with his own band.
"Well, when God phones you up, you've kind of got to go really," says Carrack, going on to reel off the band - including bass guitar legend Willie Weeks - and a tour schedule that took in ten nights at the Royal Albert Hall and gave him, he says, a great experience.
Somewhere along the way Carrack found time to record a new album, Rain or Shine, that features five new Paul Carrack songs and pays homage to heroes Bobby 'Blue' Bland and Ray Charles, whose music he grew up with.
"I'm not trying to reinvent the wheel as a songwriter," he says. "I go for two verses, a middle bit and a chorus and trust that the delivery will make people want to listen to me and radio presenters will feel they want to play my music.
"Radio's very different now. Back in the days of How Long, you could get a play here and there and it might catch on. Now it's all playlists and very scientific. But I still get a kick out of hearing my voice on the radio. It helps remind people that I'm still alive and out there working."
Paul Carrack plays Glasgow Royal Concert Hall on Friday January 10 and Queen's Hall, Edinburgh on Saturday, January 11.