This is pretty much in line with the brief explanations he’s given recently, although a bit less politic.

I find his example problem to be a bit odd, given that the last time he spoke on the subject he said he had no problems with any of the cast or crew, but who knows.

I’m sure there’ll end up being wank over the indirect aspersions possibly being slung at other actors who have worked on the show; I’m not really sure what to think about that yet, especially taken in context with the rare comments the other actors who were around at the time have made.

I really just want a straight answer about this. 

Okay, so I guess the text-analyser in me can’t shut up, so here’s my annotated/paraphrased version of what Chris revealed.

He said he left because of his social/political ideals:

I left because of politics. I did not see eye-to-eye with them. I didn’t agree with the way things were being run. … So I left, I felt, over a principle.

He said that some people at the BBC (including one director) were creating bad work conditions for members of the crew:

I didn’t enjoy the environment and the culture that we, the cast and crew, had to work in. I wasn’t comfortable. I thought, ‘If I stay in this job, I’m going to have to blind myself to certain things that I thought were wrong.’ (source)

You know, it’s easy to find a job when you’ve got no morals, you’ve got nothing to be compromised, you can go, ‘Yeah, yeah. That doesn’t matter. That director can bully that prop man and I won’t say anything about it’. But then when that director comes to you and says ‘I think you should play it like this’ you’ve surely got to go ‘How can I respect you, when you behave like that?

His parents and brothers are working class, that’s his social background. He said that staying there despite the work condition problems would make him lose his integrity and show disrespect towards his own family:

If you allow your desire to be successful and visible and financially secure … to make you throw shades on your parents, on your upbringing, then you’re knackered. You’ve got to keep something back, for yourself, because it’ll be present in your work. A purity or an idealism is essential … you’ve got to have standards, no matter how hard work that is.

He doesn’t expand on this here, but in many interviews you will find that his parents and brothers are all “working class”, just like the crew. My interpretation is that he grew up with this social background, and ignoring problematic working conditions, specially for the “working class” people on the show, would be like turning his back on his family.

Unless he named names (which would be petty of him) or went into specifics about various events (which was not the goal of that Q&A), I don’t see how much clearer he could be. From what he says, he chose his ideals over money. That was the right thing to do for him, and he didn’t do it because he disliked his role or the show or the fans:

The important thing is that I succeeded. It was a great part. I loved playing him. I loved connecting with that audience.

I wish Doctor Who fans would concentrate on this last part, rather than on the utterly personal reasons for Chris not to do a second season. It’s obvious that it was a hard choice for him (“So it makes it a hard road, really.”).