Just noticed them today when I was in Sainsburys Edgware store.
These are the standard 330ml Cans, which had been produced for the Jewish festival of Passover and can be found in the Ethnic section
Taken from Wikipedia:
Kosher Coca Cola, produced for Passover, is the closest formula to the original that can be purchased. It is sold in 2-liter bottles with a yellow cap marked with an OU-P, indicating that the Orthodox Jewish Union certifies the soda as Kosher for Passover, or with a white cap with a CRC-P indicating that the certification is provided by the Chicago Rabbinical Council. While the usual Coca-Cola formula is kosher, during Passover Ashkenazic Jews do not consume Kitniyot, which prevents them from consuming high fructose corn syrup (HFCS). Even sugar-based formulas would still require certification of both the formula and the specific bottling plant, as the strictures of Kashrut on Passover are far higher and more complicated than usual kosher observance. This variety is also consumed by some who view sugar-based cola as tasting better and more natural than HFCS-based soda