Series 9 Episode 7 discussion

[WhiteSwan]

After having just watched the whole of the episode I really would like to ask the writers some serious questions. Some of them have already been mentioned, like e.g. the switch of someone's personality from evil to good and then back again in an instance. And the more technical question about mobile phone networks and types of mobile phones in 1995. But there is also a new question which occurred to me: why on earth would someone who apparantly is a killer, someone without any conscience, someone who just blew up the British embassay (why he did it would be one more question) and then murdered his friend to get his passport join MI5? I mean come on, he had the passport, so he managed to leave the country - he could have gone anywhere, he could even have gone back to his old life (with the danger of being blackmailed by Vaughn, but as it is that happened anyway). Would anyone who's on the run and who's trying to cover his tracks join MI5? Is this a well-known safe-haven for criminals? Looking at the way they are vetting people it probably is, but still.
So either there is much more behind it and maybe even Harry is involved (why would Lucas want to talk to him alone, didn't he say his only interest was to be with Maya? So why bother about Harry?) or this series is really turning into some sort of ridiculous soap opera without any credibility whatsoever.