I liked it. I didn't mind that some bits of sub plots seemed extraneous because ultimately there were either points to be made, or connections that snaked through the weeks.
Jane and David knew each other and had some kind of history. I had thought they were related in some way, but now not sure about that or quite what it was. He'd done her the favour of signing Linh's paperwork, not knowing she was in the UK illegally. She was the witness to the shooting of Abdullah, on the doorstep of Karen's home. Karen being David's ex.
Quite apart from the assassination, we already have Jane conflicted between the church, her sexuality and her lover and David conflicted by his party politics and towards the mother of his child plus his child's welfare and Karen's personal issues, whatever they actually stemmed from. Ultimately Jane chose the church and David cut loose from Karen, emotionally at least.
Perhaps this strand was all about conflict, using people and letting them down? Undeniably Sandrine was let down by her mother, her superior officer and the family friend, Peter? who rang the 'travel agency' and ultimately by Kip too with her accidental slip of the tongue 
She was such a sad character despite being the killer.
The scene with Sandrine and the Major's wife was good too. I'm sure she knew all along exactly what her husband was like and he used her to maintain the status quo. In the end, being confronted by Sandrine, she came to her senses and she 'let him down' in a sense, by finally seeing just what their relationship was based on and throwing in the towel. I suppose you could say Peter, the family friend, also let down Sandrine's mother, who had now lost her husband and both children.
That's without starting on the pizza parlour, the refugees, the police and MI5.