Thanks again, Scifan57.
Emoji has always been to the right of the ABC/123 key until yesterday, as per iphone 8, and the update to ios12. I am pretty certain of this as I do my Italian exercises each morning, (practical rapidly approaching...) and a diary, which uses numbers and a tick from the smiley keyboard.
I tried the USA setting you suggested and also, back with the UK keyboard, deleting and reinstalling the Emoji keyboard. Both times I did an iPad reset. When I reinstalled the Emoji keyboard it went back to being in the wrong place.
While it may possibly be some sort of conflict, I have submitted a bug report to Apple.