As I understand it, and from that article, the ISA (Intelligent Speed Assistance system), will have an On/Off switch that that auto resets every time you re-start the car (much like a load of folk currently do with the stop / start system), so it won't "force" you to slow down if you don't want to, however here's the rub and the more worrying consequence for speeders:
So it'll still be a free-for-all for speeding motorists then? Not quite. Under the new rules, cars will also be fitted with compulsory data recorders, or "black boxes".
So if you have an accident, the police and your insurance company will know whether you've been going too fast. If you've been keeping your foot down and routinely ignoring the car's warnings, they may take a very dim view of your actions.
In fact, it's this "spy on board" which may ultimately have a bigger impact on driver behaviour than any kind of speed limiter. It's easy to get away with reckless driving when there's only a handful of traffic cops around to stop you. Much harder when there's a spy in the cab recording your every move
So, if you do choose to speed then get caught by the Police or most unfortunately be involved in an accident, both the Police and the insurance companies can use the on board "black box" to find out what you were doing and either prosecute you or have your insurance null and void if you are found to have been speeding and ignoring the in car warnings.