Shaka Zulu
I think you have missed the judgement here - the judge has ruled on the February ballot results, which was the basis on the March strikes. Thus the march strikes (assuming the appeal fails today) were also illegal and potentially leaves strikers very open to the jobcentre.
The recent ballot was no more than a straw pole and has no relevance in law - it was just for the Union propaganda basis (as they knew that anyone left in the union would still be favouring their point of view, whilst if people generally didn't they have resigned)