The animated Mr. Cube takes a bow in From Cane to Cube.
Advertising and propaganda have always been two sides of the same coin. When the Labour government declared its plans to nationalise the sugar industry in 1949, however, the two converged entirely in the creation of Mr. Cube.
David Kynaston summarises the affair in his book Austerity Britain:
The most memorable anti-nationalisation campaign, however, was that waged by the sugar monopoly Tate & Lyle. An animated cartoon character, 'Mr. Cube', was created in July 1949; for the rest of the year and into 1950 the little man seemed to be everywhere. Daily he was to be seen on sugar packages, on ration-book holders (given away free to housewives) and on Tate & Lyle delivery trucks, while intensive advertising in the press was supplemented by shopkeepers handing out millions of leaflets to customers. 'Take the S out of State,' was one of Mr Cube's easy-to-grasp slogans, 'Tate not State!' another... Altogether, it was an astonishingly effective, American-style campaign, which the government was quite unable to counter.
I don't know if this account is correct in implying that Mr. Cube originated in animation, but he was animated at least once during this period: the 1950 Tate & Lyle promotional documentary From Cane to Cube opens with some short footage of the character..
The character was around for quite a while after the nationalisation debate. Google Documents contains a 1962 pamphlet entitled Mr. Cube's Roots: The Story of Sugar. I distinctively remember a sword-wielding Mr. Cube being discreetly tucked away on the backs of Tate & Lyle Golden Syrup tins well into the nineties, as well, although he has since been removed.
There seems to have been a recent effort to revive the character: The YouTube account on Manchester's Grow Communications has an animation test of a CGI Mr. Cube.
The artist who created Mr. Cube was called Bobby St John Cooper, but a search on Google turns up no evidence of further work from this individual.