My instinct to call immediately proved correct.
Helpful agent, initially only offered rerouting LCY-AMS-TLV but convinced them they had an arrangement with ElAl and got the last seat on my preferred flight in J (originally avios booking in euro business, now on the Dreamliner with a flat bed, not the worst result!!)

also got the agent to confirm usual avios terms apply which is great.

thanks CWS