Yes. Strangely my post disappeared before I could edit it.

It was an ironic error.

It wasn't an error, it was a light hearted remark. I'm quite aware he didn't wear American clothes, it didn't need to be pointed out to me.

Just a little info on The Sweeney,
Carter and Regan's characters were given a specifically 'transatlantic' look (softer jackets and poloneck jumpers being the prime examples) in an attempt to give the show a look closer to Kojak ( an absolutely huge ratings success for the BBC at the time, the Regan/Carter dynamic was supposed to echo the Kojak/Croker relationship) and also to distinguish the characters from their superiors (always in a more English tailored wardrobe, again echoing Kojaks relationship with his superiors).
Just compare the wardrobe of the pilot 'Regan' shown as part of 'Armchair Cinema' strand and the wardrobe in the series, the difference is very evident.
This even had an effect on the choice of vehicle (Ford Consul GTV6, the most American looking car produced by FordUK at that point) and the choice of booze (the pilot beer and the series spirits usually whisky).
Thames TV always had an eye on overseas sales for their shows and quite often made subtle changes for the transatlantic market.
The look may not be 'Ivy' but it has a very American edge.

^ Kingstonian, I know I'm straining the credibility of the point, but as Mr. Yuca decided to embark on a bit  pedantry towards Mr Slacker I thought I might as well be a little pedantic over the origin of the Sweeney.
I make no claims to it being sartorially good, but it's American influence was very evident in-particular it's 'anti-hero' lead characters and the choice of vehicles and booze  (compare it to other UK detective shows of the same period, and it's positively dripping with the influence of the then 'groundbreaking' Kojak even down to the structure of the episodes including the 'melancholy 'end theme').
Your point about it being 'Geezer' territory is very valid, as I wrote earlier the Met at the time had more problems with the casual attire on duty aspect of the show than any of the prejudice, misogyny and boozing on show.
Americans dressed as stylishly bereft as the Brits during the early 70's IMHO (the point about Halston is very accurate, following the introduction of the tonally matched tie and shirt on the fashion runway in 71/72, it went worldwide in a matter of months).

"..meanwhile at the station there's a couple of likely lads, who swear like hows you father"