Adjective indicating the state of being in shambles. The OED’s first cite is from 1970 (The Times) but curiously notes in small print: “Reported to be ‘in common use’ in 1958.”
To which I say, Hah! A Google Books search reveals a few dozen pre-1958 uses, the earliest being this from a 1939 issue of The Journal of Land & Public Utility Economics (and the telltale quotation marks indicate it’s a very early use indeed):
If judges are hesitant to adopt the findings made by a commission, and instead substitute their own inclinations, the administrative agency becomes not symbolic of legal progress but “shambolic.”
That is an American journal (don’t know the nationality of the author), but shambolic is nonetheless definitely a Britishism. Google Ngram data suggests it is currently used about five times more frequently in British than American English. But it is also a Not One-Off-Britishism: that same Ngram chart indicates frequency of use in American English has increased some 400 percent since the early ’90s.
Despite its shambolic start, the euro is not going to vanish. (Paul Krugman, New York Times, September 20, 2000.)/Taken together these albums hopefully represent the first unified volley in a new Philly sound — shambolic, shamanistic and completely cool. (Associated Press, August 15, 2011)
notoneoffbritishisms.com 
I for one really don’t like the word ‘shambolic’. I think it is pretentious and stupid.
It has definitely become a cliche in American writing about rock music, but I don’t think I’ve ever seen it used in a non-musical context.
The remaining medieval parts of some English cities (I don’t know of any in Scotland/Wales/NI) are called the Shambles, the name apparently being originally used for streets where butchery was the main activity
This word was in very common usage in the UK in the 1960s and 70s to my knowledge, and has recently spawned omnishambles, courtesy of the TV show The Thick of It, as a polite version of governmental clusterfuck