Any idea if the aircraft was G reg or something else?
With a freezing level at about 3000ft and intermittent precipitation they'd likely have been in significant icing at 4000ft so a descent to 2300 sounds plausibly like a descent into warmer air.
The puzzle is why a relatively powerful aircraft like that wasn't being flown at a more credible altitude above the tops if they were indeeed at 5000?