Can I just check - is it right that the fridge temp should be 0-5deg. Mine today is showing as 4.5 (nearly as warm as it can be if I'm right) and the jelly is frosted over and a small piece of ice just fell out of the milk. Surely it's too cold

Yes it is 0 to 5*C it's supposed to be.
(Actually I've got a feeling it's 0 to 8*C but that 0 to 5* is better... no idea why that's suddenly pooped into my head though...)

I'm wondering if your temp gauge is broken - my fridge is usually at 2 or 3*C and my milk doesn't freeze nor do I get ice in anything else.

Might it be worth you trying your freezer one in with your fridge for a while just to check them?

Your fridge shouldn't be freezing at 5c...

Are you checking the temp after you've opened and closed the door a few times?

That can make a huge difference to the temp which can very quickly go up.

Maybe the milk is your overnight temp when the door is shut for 12 hours...