So what changed their minds?

Any e-mail you send can be intercepted and read by the authorities.  Ditto any text message.  They also have the ability to know what internet sites you visit.  So where are we talking about - China?  Syria?? Iran???  Well no, actually, we're talking about here!  The Government intend to introduce legislation which will give GCHQ precisely these powers.  The only saving grace is that in order to do this, they will need to get a warrant - although I can't say that that proviso does much to make me feel easier.  In my experience, official requests for warrants are rarely refused.  What's interesting is that the last Labour government proposed something very similar, and back then the Tories and LibDems violently opposed it.