I'm referring to this article on the Guardian.
I'm wondering because it seems that despite it being a parliament computer, it appears that it was his to use - i.e. not a shared device. I would understand if other people might be exposed to such content without their consent, but it appears not to be the case. Moreover, it's not like he had a 9 to 5 job, or some sort of obligation to work a fixed number of hours, so that watching pornography would effectively reduce that amount.
The paper also mentions that he's under investigation for inappropriate behaviour towards a conservative activist - now this seems to be something serious, the reason being that there is/might be an actual victim (might be because I don't want to draw conclusions before an investigation is over).
The only other reason I can think of is that he stated that he did not view such material. But for some reason I don't feel that this is what people are worried about. Otherwise for example the title of the articled mentioned above would have been something like "Damian Green lied about ..." rather than what it is.
So my question is: why is it a big deal if a government minister watched pornographic material on their device?