“East/North” tab from Tools>Add node and against “Projected coordinates:”
inputting full coordinates from the BNG origin, such as “474795 178597”
(Eastings metres before Northings) works, so far as I see. Anyone having
100-Kilometre two-letter grid references would need to use an OS to Cartesian
appreciate this is not using “Jump to position” but it will get you to where you
want to be at the expense of having to delete the node created, only.