I also live in the uk and my yellow bellied slider has lived outside in my Koi pond all year round now for three years, He was fully grown before he went out for the first time.Before that he just went out over the summer. He now hibernate's over winter on a shelf in the corner of the pond.
As long as the pond does not completely freeze down to the bottom (which it never should)
Which means the water is warmer than you think. Just make sure he isn't fed for a few days before it gets cold, so he belly is empty otherwise he'll bloat and die.
As long as the pond does not completely freeze down to the bottom (which it never should)
Which means the water is warmer than you think. Just make sure he isn't fed for a few days before it gets cold, so he belly is empty otherwise he'll bloat and die.