Anyway, an update for everyone.
The water pump has been changed and the electricity consumption is now at reasonable levels.
Initially the water pump company insisted that there shouldn’t be a problem and when they came to inspect, they couldn’t find any fault with the old water pump. It’s only when I insisted that the electricity consumption drops significantly when the pump is switched off that they started to consider the situation.
It seems that there is some issue with certain old water pumps and the new meters. It could be that certain water pumps constantly consume electricity regardless of whether it’s pumping water or not and the old analogue meters were unable to pick it up. Hopefully this experience will be useful to anyone else finding themselves in the same situation.