Ok, thanks to Chris there. I've done some searching and think I can see the problem.
It's a matter of nomenclature, that is, they keep moving the goalposts.
We're both right. Many single ovens, even with a grill, are still, as I maintained, less than 13amps.
What I have found is that some of them, even less than 13amps, say they should be hard-wired.
Looking deeper, they specify hard-wiring as connection to a 13amp fused spur (which is run from a standard socket circuit.)
There's the discrepancy. I was rattling on about connections to a cooker point, which is definitely not needed in most cases.
I can see why. Taking 13amps via a plug will possibly cause eventual overheating of the plug, even though it has a 13amp fuse.
Silly isn't it?
So, I guess anything over 2.5kw has to be connected to a fused spur to avoid plug burning. My own oven is 2.5kw, and plugs right in to a socket.
CW, do you have a socket near where the oven is going?