When descending a slope with HDC selected the handbook says that the descent speed can be
varied by the +/- cruise control. This does not happen on mine, even at very slow speed. Does
anyone know why? Is the gradient of the slope a factor?

I tried this on mine in a multistory car park and it worked a treat - at least to slow it down anyway.

I am guessing that if speeding it up it will only go as fast as the car will go under its own momentum on the slope dependant on gear etc.... i.e. it it uses engine breaking as well as the abs to slow it down, but i can imagine that it will not introduce more revs to speed it up.

Were you trying to speed it up or slow it down? Maybe try using it to slow it down and see what happens? Freelander 2 TD4 Auto, SE, Narvik Black, Alpaca full leather, Rear Headrest Entertainment System, 6 CD, 18 HSE Wheels, Privicy tints

I tried both speeding up and down, from the default 4 mph, but no change in speed.

You have to keep the button(s) pressed when you tune the speed, until the desired speed is reached, and then release the button. Not just short pushes.
Also, when you increase the speed, in time, the speed will slowly decrease back to a default speed. I've found out that this default speed is about 8 km/h (5 miles/h).

Thank you Alex its working as you said.