I recall it being used from about 1950, defined as 'cake and arse'.
It derived from C&A, an international chain of clothing stores, with its head office in Brussels. It has branches in Austria, Belgium, Brazil, Czech Republic, France, Germany, Hungary, Luxembourg, Mexico, the Netherlands, Poland, Portugal, Spain and Switzerland. Its brands include Clockhouse, Westbury and Your Sixth Sense. The company was founded by the German brothers Clemens and August Brenninkmeijer in 1841 in the Netherlands as a textile company, taking its name from their initials. For many years C&A stores were also a standard fixture of high streets in the United Kingdom. However, the company's strategy of selling budget clothes from high-rent city centre stores made it vulnerable to a new breed of competitors operating in cheaper, out-of-town locations; these included Matalan and the rapidly expanding clothing operations of supermarket chains such as Tesco and ASDA. In 2000, C&A announced its intention to withdraw from the British market; the last UK stores closed in 2001.
Around 1980 there was a joke that women's knickers from this store were printed with a C on the front an A on the rear, (signifying 'cunt' and 'arse'), to show which way round they were to be worn.
You don’t want your friends to know you shop at C&A, but if your hand’s lucky, you might fool the less savvy into believing that the crap you’re wearing cost two to three times more than it really did.
—Yeah, thanks. (Thinking: If you only knew how little I paid for it at C&A…)