NEC is an acronym for the National Electric Code, which is actually a PORTION of the National Fire Protection Association standard #70 (NFPA 70). The NFPA themselves are an international body, not a goverment agency, so technically they could be considered relevant to the UK, but only if other authorities in the UK say so. For the most part though, it is relevent only in the US. Canada has the CEC (Canadian Electric Code), which is based upon the same NFPA 70 standard, but there are some significant differences (mostly because Canadians are constantly needing to prove to the world that they are NOT part of the US).
Here in the US most, if not all, govermental regulation agencies covering electrical work adopt the NFPA 70 standards as their own, and then a few larger entities will add some specific local codes to them. For instance in California where I am, there technically is a California Electric Code, but it starts out by first adopting all provisions of NFPA 70, then just adds a few extra pages with reqirements having to do with specific installations and materials. Since the vast majority of agencies do the same thing, NFPA 70 is called the National Electic Code, since if you abide by that, it will apply virtually everywhere in the US.
As many people find out the hard way though, the real final say-so is what we refer to as the AHJ, meaning the Authority Having Jurisdiction, at any given installation. If the AHJ happens to disagree with some provision of the NEC, they can add requirements or ingore violations if they so choose.
"Venditori de oleum-vipera non vigere excordis populi"