I noticed on Emmerdale last week that the "soap opera effect" on the picture was more pronounced than usual. Worse still were horizontal fuzzy lines around the edges of moving areas of the picture (interlacing?). Rather like this.

At first I wondered if it was our Sky Q box, which we had installed recently. The Emmerdale episodes were recorded, however I noticed the issue again tonight on the ITV news which we were watching "live". The weather forecast that came on straight afterwards looked fine though, and I haven't seen the problem on other channels, so I guess it's an issue with ITV? Has anyone else noticed this or know what's going on?

Is this ITV HD or SD (or both ?)

Which ITV region ?

It appears on recordings too, can the problem be 'frozen' ?

From your description, seems to be a de-interlacing problem/artefact

I'm not familiar with the Q box, can you force the output resolution, presumably it's set currently to 1080i (or maybe 1080p ?)

It's ITV Wales HD (103 on sky). It hasn't happened enough to spot a pattern yet, but has been noticed on both recordings and "live" TV. The recordings have been deleted now but if I see it again I'll pause it and take a photo to post here.
We've had Sky Q for a few weeks now but only started noticing the problem end of last week.

All seems very odd and would suggest a setting on the Sky Q box.

I watched the programmes you mentioned and did not notice the same artefacts.