No, grade 3 is Monitored with Police response and in order to do this has to be under a service contract with an accredited company. The grading is always defined by the lowest denominator and so that would be defined by the service contract, none = grade 1.
As you know a grade 3 is not in any way necessarily any more secure than a well installed grade 2 system. The door contacts are the biggest downfall to the reliability of grade 3. Personally I would always the necessity for full grade 3.
The idea of grading was so that there was more clarity between the insurance companies and the installers. It didnt really work because insurers who do not understand the technology will always take the highest number to be the best, which you and I both know is not the idea of grading. The problem is not all installers are the same and so the insure cannot trust the installer to install the correct devices in the right environment, because unfortunately some are clueless, or employ clueless surveyors. Sad when you think of it, this industry could be so much better.