Castor Cracking Group (CCG) was a demo group from Sweden, and were active on the ZX Spectrum during 1986-88. They were one of the first groups for the ZX Spectrum with their release of Castor Intro early in 1986.
Originally they named themselves after Castor in the constellation Gemini, but despite having "Crack" in their name, they actually (at least according to themselves) never cracked any software.
Technically, their demos were not very advanced - they even programmed many of them in BASIC and compiled the result for release. However, their significance lies in their early entry onto the scene.
UK Lead was a label used by Castor Cracking Group for the more "serious" projects. The only two projects released were Spectrum Juggler and 99Y.