Right rolls up sleeves thanks to a new born baby and a very bad back, I've had a few days to come up with my theory of what the heck is going on, here it is!!
Ros's children are adopted, they witnessed a crime when they were little and have lived with her under Witness Protection ever since. Hence her career break when they were young, not babies. Jimmy Lakewell was the childrens' solicitor and knows the full situation. Nick Huntley was in prison at the time (possibly sex offences or money laundering) so wasn't around for the adoption and doesn't know why the kids are in WP.
Roz suspects Nick of involvement in deaths of Basminder and Leonie, and so, with assistance from Jimmy Lakewell they conspire to frame vulnerable Michael Farmer through the fake kidnap of Hana Reznikova. Balaclava Man is a red herring.
Tim Ifield had been secretly investigating Operation Trapdoor for sometime. He only officially joins the case with Hana's kidnap. TI dies when Roz tries to fight him off, and his jugular is nicked in by the saw in the scuffle. She calls in her kid's liaison at AC-9 to assist in the clean up and Tim's subsequent framing. The computer will have recorded her ringing the doorbell that's why she takes it, plus his fingers.
As AC-12 continue to investigate Roz, AC-9 plant JamienotJames undercover in the team. He is deliberately crap in the interview to protect Roz and undermine the investigation into her.
Hilton whilst slimy is not part of the clandestine group of corrupt police officers. He is aware of the full picture re witness protection of the children and the steps AC-9 have taken to protect them. He's unsure whether he can fully trust Ted with the whole truth because he is so black and white in his attitudes. Dot's dying declaration gives him ammo to remove Ted when he persists in investigating. Maneet has been told enough by Hilton to get her to feed him information from AC-12 directly, so he's not just relying on AC-9. I would bet that the Head of AC-9 also has a surname beginning H and Hilton is investigating them covertly too.
The post-it was left by an undercover AC-9 officer placed on the Trapdoor team. My money is on the uniformed PC who seems to see everything.
OK mumsnet, tell me what you think!