This could suggest that it's not UJ joint that is not the issue then ?.
How many bolts did you tighten then Ian.
There should be two bolts that secure the outer steering column assembly to the body shell and then you have the single nut, that when tightened applies more pressure to the manual pinch clamp adjuster.
Not sure if you are aware, but there is one more other single column bolt that secures the steering column, but it can only be accessed from under the bonnet and you need to remove the wiper blades ( puller ) and the wiper scuttle panel first.
This single bolt passes through the main baulk head first, then secures the steering column assembly.
You maybe just able to see the tail of this bolt from under the pedal box inside of the cabin.
But it can only be tightened from under bonnet as you are unable to turn the welded nut.
One member did tighten the three same bolts, but after a couple of days the rattle came back.
He then went after the third bolt ( under the bonnet ) and it provided the fix.
Somehow the preload on the manual adjuster appears to lose it's tension after a while.
I tend to use the steering a lot, to aid me to enter the car due to a very painful right knee.
This extra pressure may be the cause of the sideways movement that is present at the steering wheel ?.
The clicking / ticking / single knock ( what ever you wish to call it ) is definitely emanating from the head of the steering column at about the 1 - 3 o'clock position I have personally found myself.
There is no feeling of any free play at the steering wheel or any vague steering wander etc.
Any symptoms in this regard, need further investigation urgently as the UJ could be an issue.
@IanE Please keep us informed on the outcome of your work.