After trying many web and Edinburgh trade sources I solved the problem for my dripping Blanco Cleo 6100 as follows: after ckecking length and width buy spare ceramic cartridges from B&Q plumbing spares then modify. A wide barrel flange on the spline end of the B&Q cartridge prevents its full insertion Of the tap cover. File the around 1 to 2 mm of the flange to the same diameter of the shaft adjacent to the spline, leaving enough flange to support the spring clip adjacent to the ceramic barrel. The cartridge then snugly fits into the tap. Hey presto! You have saved loads of dosh and it works perfectly. I used a combination of a narrow Dremel grinder wheel and a needle file to get this perfect result. Ps. Make sure the ceramic disk is perfectly clean of grind/ file bits before inserting into tap.
Dickybird
May 2013