Bought a spare wheel hub, unpacked it, & double checked
it was the correct size/type by fitting it into the spare wheel,
.... no go, WTF!.
Spare wheel rim looks exactly same [alloy, white, same style etc]
as wheels on axle, so I would guess it came with the trailer from new.
The only difference was the tyre [unused].
After some thought I realised I was presuming the spare was also same 'size'.
... pulled a wheel off the axle & the new hub fitted it perfectly !?.
Measured PCD [info from cormorant post] & it seems the trailer has
- 13" Ford Wheels on axle &
- !3" HT as a spare
BMT all 2002.