The difference may be accounted for by the camera setup. Hollyoaks is filmed with a single camera, and Hollyoaks Later is filmed with multiple cameras. From Wikipedia, with a multiple camera set-up,
...multiple shots are obtained in a single take without having to
start and stop the action. This is more efficient for programs that
are to be shown a short time after being shot as it reduces the time
spent film editing or video editing the footage...Drawbacks include a
less optimized lighting which needs to provide a compromise for all
camera angles and less flexibility in putting the necessary equipment
on scene, such as microphone booms and lighting rigs.
According to this an interview with actor Neil Newbon (Walker), the single camera gives Hollyoak its dramatic feel:
Hollyoaks is still the only soap that shoots with only one camera, we
don’t use multiple camera shots across one another, and we shoot like
a drama and because of that we are unique, it has more of a dramatic
With single camera, every time the camera has to be moved, the lighting people have time to set the lights just the way they want them.