By Kieren Williams & Sam Elliott-Gibbs Brits have been told to brace for temperatures plummeting to -10C making parts of the UK colder than Greenland next week. Warnings have been issued to the vulnerable as a plume of Arctic air will bring snow and spark sub-zero conditions in the coming days. The lengthy spell of cold air comes down from today, the Met Office has said, with the mercury projected to tumble. The forecast has prompted the UK Health Security Agency to issue an amber level cold-health alert. A blizzard could hit Britain within hours at the beginning of a freezing week already pac…