I found this picture in the photo gallery here.
It shows the gearbox end of the speedo cable and illustrates whar Eric said that the cable can be unscrewed at the gearbox, without having to remove the angle drive itself.
What is not quite so obvious is that the gearbox end of the cable is similar to the speedo instrument end. The inner cable is squared off at each end and is pushed into a square hole in the moving parts at each end. What Les has done is, from the top end managed to pull the squared end out of the angle drive at the bottom end.
It should be possible as I said above, to push down on the inner at the instrument end, while jiggling/rotating it around a bit and have the lower end slip into its square hole.
Should that not work it is not difficult to jack-up/ramp the car and crawl underneath to unscrew the bottom end of the speedo cable (pipe grips may be needed), if the inner is not then poking out of the outer tweak it out with fine nose pliers or get someone else to push down on the inner at the dashboard end.
When the inner is poking out; you can (with a torch/head-mounted lamp) see the square hole in the angle drive and you can push the inner into it, then screw on the outer. Then back at the dashboard the inner should be poking out just enough to fit it into the speedo square hole (rotate the speedo to & fro a little until it fits) and then screw on the outer.
The description might seem long & tricky, but actually it's an easy job. I have done it alone a number of times.