Thanks - basically I engage cruise and it displays SET on the display - however, on going downhill, speed increases. So on one hill near my home on an A road with a 30mph limit and a camera sometimes half way down, I set the speed at 29 but by the time I reach the bottom of the hill, I am clocking 37mph. So despite cruise saying SET, it doesn't set.
Just can't understand the explanation of being a Lexus safety feature ?