I've noticed I have judder (especially on the HD channels) when using the channels app on Apple TV. I have a feeling it is due to PAL being 50hz. If I set my Apple TV to 50hz it is much better but everything else on Apple TV is awful.
Is there anyway around this for us UK folk?
You can set it to 50hz and then enable frame rate matching so other apps switch to 60hz
Been a while since I've used Channels on ATV but has the option to auto switch frame rate within the app been removed then?
Thanks, I've done that 
I've been playing with the settings for an hour or so but now I seem to have a stutter that occurs every 10 seconds or so.
Any chance this could be a HDMI issue?
I believe so. I only see an option for SDR switching.
Just to update on this. I believe I've solved it. I swapped my HDMI cable to a new high speed one (which seemed to have fixed vertical tearing I was experiencing on everything) and also tinkered with my TV's settings (Sony's film mode and motion settings - medium and standard) and it seems spot on now after letting a channel settle for a minute or two.
This is happening again. I believe it's linked to the deinterlacer on ATV as my Android phone is perfect.
I get this when 1st opening app after ATV is woken from sleep. If I back out to home page & reopen, it's then ok after seeing screen go black as it sets correct frame rate, which it doesn't on 1st go.
I think it's how Channels handles UK/50Hz TV in general. I see the same behaviour on my Nvidia Shield if I use software decoding. Hardware decoding works fine. The trouble with hardware decoding is that it doesn't understand aspect ratio changes, so 4:3 programmes end up getting stretched. Not sure if the Apple TV supports hardware decoding of interlaced content; I vaguely remember that being called out as a limitation?
I know there's an option to stretch 4:3. With me Quest HD and Channel 4 HD (+1 HD included) are the worst.
I noticed the black screen you mentioned @Stuart_Fagg but it doesn't seem to fix anything on these channels. I've tried both interlacing options.
A good programme to test is A Place In The Sun.
I've suffered with the same sort of problem on and off over the last year. I suspect it could be the deinterlacing as I seem to always notice it on 1080i channels. Weirdly it doesn't happen all the time but when it does a skip back usually solves it, annoying as it's about the only problem I ever had with Channels.
Channels : is there anything we can do to help debug this?