Slowly working rounds the issues on my new-to-me 1988 (UK built) XJ6 (XJ40).
Got the brakes and wheel hub sorted, so today was the first drive to work and back. I had noted that the column seemed to telescope out, to give me room to stash my long legs, but it did not seem to lock in place.
Research at work mentioned some wheels telescope, and later ones tilt, but there should be a lever/clamp/something to lock it in place. I had had a quick look under there a few weeks back and had seen nothing that looked a likely candidate.
Tonight I got down on my hands and knees, with a flashlight and worked out that someone before me had removed the trim piece that would be over the drivers knees, moved the lever to the down/release position and then reinstalled the trim piece, effectively hiding the release lever. Three screws out, trim off, lever up, trim back on and I have now got a working telescoping column.
Hopefully no one else ever has this issue, but at least it is a cheap and easy fix.