Chris Tolley (ukonline really) writes:

No, the cameras are there to enforce the speed limit. That is all they
do. Someone could be driving their car sideways, but within the limit.
It's your assumption or the assertion of others that cameras monitor
safety. And it's a flawed way of looking at it.

But as has already been pointed out, the speed limit can depend of the
class of vehicle. Speed cameras only enforce the speed limit for those
vehicles subject to the highest limit at that location. So if a vehicle
is travelling faster than the limit which applies to it but slower than
the limit which applies to the least restricted class of vehicle, the
camera will not detect that is exceeding its maximum permitted
speed.