He's dressed pretty much like a late 70's early 80's Skin (before the nationalist subset took control)
This was basically a culmination of the Punk, Ska and Punk movements fusing into one.
Note the crombie, top buttoned shirt, pleated pants and Doc Martens.
Makes sense when you consider that Capaldi was part of the Glasgow Skin/Punk movement.
He and Craig Ferguson were even in a band together believe it or not.
It was also the look Rik Mayall sported in The Young Ones.
It might look odd because it's from an often overlooked movement that was co-opted by Nationalist idiots.
So the whole Skin thing basically gets hand waved as being racist and of no worth.
When at one point it was a fusion of counter cultures and rebellious youth coming together as one.