It surprises me how supine governments are when dealing with these big tech companies. If I were in charge and Facebook refused to comply with a request for a terrorist's comms, I would 404 facebook.com across the UK as soon as the necessary blocks could be put in place. I imagine you'd have those comms in your inbox within half an hour.
It would be more likely that you would have a population up in arms and asking themselves if they will need to bring their own tar and feathers to the 'run these idiots out of town on a rail' party. Facebook is far more popular in the UK than any politician or party and I think the only thing that would happen within half an hour would be to table a vote of no confidence.
As if. The populace are even more disempowered than the government.