Its off :-)
I dusted down the old paraffin blowlamp, didn't have any paraffin
so filled it with diesel. It worked a treat. Combining that and
the gas blowtorch got the impeller much hotter and eventually it
pulled off. Had to be pulled with the puller for at least 2
inches though. It's on a 3 inch long straight shaft with a
keyway, slightly rusted all the way.
Now to fix it.