It's the CPS who decide whether or not there is sufficient evidence to secure a conviction - if they think there is they prosecute, if not they drop the case.  This is standard for all reported crimes and to be fair they don't, in general, do a bad job within those parameters.  Most of the historic crime prosecutions have been successful.

With regards to naming the accused it is not normally the authorities who do this - normally they simply report that, "a man", "a number of people" etc. have been arrested - it is the press, news organisations or social media that name them.  When they do actively identify a "suspect" they get vigorously criticised, as happened with regards to Cliff Richards.