OP, GSV is of little use at ground level. Could you look at the aerial view and indicate where you were parked.
At present, I think there's literally a turf war between the council and the hotel.
You were parked somewhere on the private property (AKA hotel car park and ancillary areas) which is controlled by a private parking operator as indicated clearly by entrance signs. The car park seems to be bounded on all sides by grass as regards which only that part which fronts The Embankment may IMO be correctly termed 'verge'. In one of the CEO's photos - which were almost exclusively taken from the private property- a No Parking on verge sign can be seen. But this is facing you and there's grass between you and it which IMO means it applies beyond the sign, not in front. If they mean in front then place it on the border of the car park hardstanding and grass.
Subject to getting more detail as regards exactly which piece of grass is involved, I don't think the contravention occurred. At worst, for you, de minimis, at best there's no order restricting parking where you were.
..and it's the wrong contravention, it should be:
Parked with one or more wheels on or over a footpath or any part of a road other than a carriageway. (Annex B to SoS's Stat Guidance refers)