MI-5 was known as Spooks over here … frankly, I didn’t think much of it. But, yes, it’s a British show.
You mean the show that I mentioned in post #11? 
I’ve read (in a book on syndicated television programs) that Callan was syndicated in the US in the early 1970’s. No clue about either of the other series.
Haven’t seen any British cop shows since i moved to the US, but back in Australia i regularly or sporadically watched:
The Sweeney
The Bill
Cracker
Prime Suspect
McCallum
I’ve seen a few episodes of MI-5 / Spooks on DVD and thought it was a pretty good show.
Let me try to answer the general question here: No British TV show has been a mainstream hit since the mid-1960’s. During the early and mid-1960’s, several British TV programs were shown on the commercial broadcast networks (which were ABC, NBC, and CBS back then). Among them were The Avengers and The Prisoners. The commercial networks then quit showing British TV shows. There was no market for them till the mid-1970’s, when PBS, the noncommercial broadcast network began showing lots of British programs. Still, nothing shown on PBS could be considered a mainstream hit program. A cult hit, perhaps, but even the top-rated programs on PBS don’t get enough viewers to be considered mainstream hits. (Perhaps the most popular British TV program in the U.S. between the 1960’s and the 1990’s was Benny Hill, which was shown as a syndicated program on many local American TV channels without ever having a national network market.)
There are now three more commercial broadcast networks (Fox, UPN, and WB), but the rule still holds that the commercial broadcast networks don’t show any foreign-made TV programs. (Does anybody know of any exceptions?) There are now a number of cable channels that do a lot of British programs, including BBC America and A&E, and of course PBS shows a lot of them, but again these are at best cult hits, not mainstream hits.
Anybody who has watched a lot of PBS has almost certainly seen a fair amount of some British TV police shows, like Prime Suspect or Inspector Morse. In general, the harder edged the British police TV show, the less likely it was to be shown. PBS loves showing British-made cosy mysteries. I don’t know if The Sweeney, The Professionals, Callan, or Special Branch have ever been shown. It’s hard to know anymore, since there are so many cable channels that it’s hard to keep track of what’s being shown on them all. The clear majority of American households have cable TV these days, and it’s not uncommon to have access to a couple hundred cable channels.