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I would say both are red eared sliders Trachemys scripta elegans.
What are the features of the front one that allow you to reach this view?
Terrapins are not my area of expertise but I'm keen to learn.
If you look just below and the sides of the left eye you can make out the end of the yellow stripe which runs to the eye (clearly visible on the other terrapin). On the yellow-bellied slider you would just be able to see the upward branching yellow mark behind the eye.
Lat/Lng: 51.63032, -0.487328
OS grid ref: TQ047934