Illegal agreed,stupid? different people have different views I suppose,my view is that it depends on various circumstances. 
Yes, you are right in my opinion Albitz, as knowing the M4, and many other motorways very well, doing that speed at 1500 on any afternoon would be achieved in heavy traffic, which makes it all highly dangerous.

120 mph at 0300 is a completely different ball game, as then it is usually just you placed at risk, although on the M4 you have still got HGV's operating in large numbers, as we have on the M20 locally.

A fair enough point Ms Zoom however, I had a back tyre blow at an indicated 115mph in an unmarked BMW - on official business - before anyone asks

and I have to say that I could have done without the fright.

Even with all the training, good fortune plays a large part in the outcome. I was kucky, the m road was reasonably clear at the time.
Speed was managable once but today, there are just too many people driving with their attention directed elsewhere, rather than the task at hand.

Excess speed will kill every time - if you luck runs out
