Well a happy ending! And a cautionary tale.
Took it round to a friend’s who put his bolt extractor (Easy Out) on it. Just as we were about to give up it shifted!
Then he asked how the EBB worked. Simple I said just put an Allen key in and twist. Nada, nothing, that was seized as well :(. Fortunately a little persuasion and it shifted. We pushed it out and all the grease had dried out. Think I need to add regular EBB removal to my maintenance list. Bike was new about 15 months ago and I spent 6 months of last year abroad so it only saw light use.