I'd be curious to see if there is continuity between N and the transformer case.
Calling something a 'European' voltage is kinda a misnomer while they agreed on a standard voltage and frequency the
grounding salad (Earthing Systems) in Europe are anything but simple.
While 400Y230 is most common in urban areas, villages and towns, you can find areas that have a 230V corner grounded delta (Norway), 220Y127 (Spain), 230/460 single phase, even 230V ungrounded you can have just about any type of grounding (earthing) you can think of.
And since the UK just standardized on paper but never changed anything they are effectively 240V.