The Snooper's Charter would endanger computer security researchers in the UK.

There might be one way around this. If you publish info about the back door you found, encrypted, on a foreign site, and send the key to another foreign site that will publish the information in several months no matter what you subsequently say or do, you might then be safe discussing the matter with some foreign colleagues with a view to publishing it in a better way with better checing.

Of course, it's nuts to make security researchers go through these steps to protect themselves from state repression.