Hi, are these photos from this month?
It would help if you could describe the nose to tail length. And head and body width to get an idea of dimensions. For GCN look for dark grainy skin texture, they look more like the traded Triturus (as you can gather from genus name). Just to add some spice, alpine newts also come from same genus so cam look very similar! And the belly is really helpful.
Ultimately - if you're unsure about disturbance and legality - contact your local ARG group. Hopefully someone is active, they may be able to assist further maybe even visit if local.
http://http://www.arguk.org/local-groups
Otherwise is it possible to trick one into perhaps a half cut a 2l bottle or deep tuberose container on its side, weighed with a stone and put loose leaves in? if you put it in an area they frequent - they just may use it, and then you'll have a chance of lifting it up and checking the belly peacefully. Or carefully lift large stones and logs - you may find one playing dead on its back and then you'll get the belly shot.
It's true that palmates tend to be found in acid environments, but I've also found then in deciduous woodland too. They are just more tolerant of acid soils than the smooth, it could also be the alpine newt (alpine - acid soils too).
To tell the difference between palmate and smooth - ideally needs to be a larger one ie adult. Then we need to focus on the rear feet and neck. really you want to revisit during the breeding season when they are males around, and the colouration and crest design will help define between all species then.
What may help with focusing the camera in the dark is to first assess the distance you want to take a shot (eg 20cm away, remembering that you can always zoom in on an image). Use your hand to set the focal length, giving the camera a larger area to find (ie place at same distance you want to shoot the newt) and half depress the camera button (most smartphones allow you to do this) and you may need a friend to help, then whilst still holding the half depressed button - reposition the camera to the newt and fully press - and hold until the flash is done.
If you find that your hand colour has caused colour wash out, try it again on something else on your body (knee? Shoe?) that is a similar colour to the subject.
Hope that's comprehensive? Typing on a tiiiny screen lol.