Ford Fiesta 1994 Ghia Ignition Barrell, & Key Replacemen

I am attempting to replace the Ignition Barrell, and Key, on my sons Fiesta which is broken.
I have obtained a used replacement for a complete unit, as I am told you are unable to replace the barrell without the whole unit.
However on stripping out all the steering cowlings, electrics, and the old ignition barrell.
I am at a loss to see any fixing method, for the rest of Igntion/starter switch unit to the steering column.
The one piece unit surrounds the steering column, but dosnt appear to have any bolts, screws. Or remains of any type of fixing.
Is it nessesary to remove the steering wheel before I can remove this unit.
Or is there some unkown trick I have missed, to replace it.
Any help would be much appreciated.