Thinking about it, Sweeney was always meant to be gritty and adult whereas Professionals was meant to be tongue in cheek and corny - it was after all, prime saturday night viewing for families and not to be taken too seriously.
I think the intention was that The Professionals was the UKs answer to Starsky And Hutch - breezy buddy-cop action/adventure. But The Sweeney was kind of a British TV version of The French Connection, with Thaw's Regan doing a pretty good impersonation of Hackman's Popeye.
They regularly show them on itv4 at 7am and i find them very much of their time. Im sorry to disagree with Mike but. When ive seen them ive found them dated and corny and cartoonish, almost for kids, and rather silly. In contrast The Sweeney still holds up well and has far more gravitas and substance.
It could be worse. Sadly, this is available through Network DVD.
