I've just discovered my least favourite job so far. I have offered up the steering tube and it appears to have engaged with the splined stub on the front axle but it won't go far enough down for me to clamp it.

Question: How much force is permissable to tap it down, and how far down does it need to be? Completely, or just enough to clamp it tight?
The pics below show the amount of space that's currently left over at the top and bottom.

Can't see any photos, do you mean the steering column the steering wheel is attached too? If so, you can push it too far on and you'll be unable to slot the bolt through the clamp. There is a notch on the column and the clamp and bolt need to be in line with that notch. Hope that helps, if I'm on the right track

What a pillock I am, I forgot to add the pic's
It's actually sorted now Johnathon thanks, and yes you were spot on that's what I was after.

Excellent