I think that the terrorist plot could be very big misdirection - it is the obvious choice for the train tickets/the Islam conversion.
I could easily think that the mother snapped and did it, went loopy and the religious stuff was a step too far, she thought she was cleaning him.
However, this doesn't fit with the 2 ex-coppers.
The mother made the call to counter terrorism to say that they were corrupting him, that they were evil. This gets him on the watch list.
The muslim girl has his baby, but doesn't tell anyone - she knows something is going on. I don't see who is in it together. Is it the mother and the coppers? Or the girl and the coppers? The coppers and counter terrorism? It's quite bloody confusing.
If I hear the words "It's EEEEEEVVVVVVVVVVIIIIIIILLLLLLLLLLLLLL" again I might kill myself.
MAYBE _ he did have terrorist leanings, not extremist views, but just coming from the wrong direction, like the guys in Four Lions I suppose. The girl is involved somehow - he relies on her to keep him safe. He gets tortured, not by the police, maybe by someone in the group who is undercover? It gets covered up. I think the mother is a red herring - she is simply crazy.