The EFJ has released a statement regarding the affair, but I can't find an English text copy of it. Here is a dutch article referencing it, google translate probably required:
http://www.nu.nl/media/3556146/europese-journalistenbond-hek...
One choice quote from all the material about Miranda's detention is this:
"One US security official told Reuters that one of the main purposes of the British government's detention and questioning of Miranda was to send a message to recipients of Snowden's materials, including the Guardian, that the British government was serious about trying to shut down the leaks"
It looks like it has sent a message alright, every journalist in the world has been made aware of how serious this issue really is and that they and their family members (active or otherwise) are potential targets. This is the media equivalent of sticking a baseball bat into a hornets nest.