From the link:
The idea that cars will be fitted with speed limiters - or to put it more accurately, "intelligent speed assistance" - is likely to upset a lot of drivers. However, the new system as it's currently envisaged will not force drivers to slow down. It is there to encourage them to do so, and to make them aware of what the limit is, but it can be overridden. Much like the cruise control in many current cars will hold a particular speed, or prevent you exceeding it, until you stamp on the accelerator.