Elmsett (EGST) airfield is missing from the iPad data set. I can create a route to it but the airfield information is missing. The information appears correctly in the PC version.

It seems to be visible here. Are you sure it's not being filtered out by the settings in the Map Layers screen?

My apologise, yes you are quite right. I had only adjusted the navigation options, not the map layers. For some reason I thought I had more diagramatic info available on the PC, but I was wrong on that.
I would have thought Elmsett was; by many criteria; as big an airfield as those mentioned previously in the Wattisham MATZ. is it AIP info that alows more information to be included?

Which setting had filtered it out, exactly?

Map Layers-Airfields-Min Runway Length needed to be "Not Set". Anything above this filtered it out.