My intention is to very much NOT go dark - but I'll incorporate ideas from a variety of sources, and even ideas from dark concepts can be used in non-dark games. In the case of this campaign there is not particular "the government is E V I L" vibe. It's just a big bureaucracy, neither good nor evil. The heroes work for a apartment that acts in tandem with the Metro Police, and they are definitely positioned as the Good Guys (rather then the Not A Bad As The Bad Guys Guys). Certain background plot elements require that they be working "within the system" - but not in a darkly depressing "there's a huge evil conspiracy within the British government that the players need to defeat", but more that there are secrets the PCs will need to uncover, and the very existence of these secrets will only become apparent to people within the system.
Plus, it provides a framework for financing, equipping, and organizing heroes who have no other reason to be together.