Will it be possible to commit a speeding offence in an electric car as the computer would over-ride the driver?

Do you mean an electric car or a self-driving car? (big difference)

Electric cars don't have artificial intelligence (i.e. they don't drive themselves) it's just a method of propulsion. The driver still has to make all the decisions and control the vehicle.

We're still a long way away from self-driving cars being the norm. The technology exists but it is in its infancy and we have yet to work out a feasible way for drivers and driverless cars to interact. It will probably have to be all or none for this situation (and people aren't ready to give up their independently operated cars just yet).

But, having said all of that, if and when we do go to self-driving cars, it will be very likely that you won't be able to speed (unless of course you hack the system which people would never do, now would they...).

The drivetrain has NOTHING to do with computers overriding the human driver.
In addition, the computer most likely doesn't even KNOW the speed limit on most roads.

It's certainly possible to make a self-driving car that would not exceed speed limits and that the driver could not override. I don't think it's possible that anyone would buy such a car.

The driver may well determine the speed the vehicle will travel at, even if it is over the speed limit but is still safe. For instance, NOBODY does 70mph from LA to Las Vegas. If you drive the speed limit you will get run over by a hundred cars. And BTW, autonomous driving is in all vehicles, not electric vehicles. The best autonomous drive in the market now is the Cadillac Super Cruise. That will be available on all Cadillacs in one or two years.

There are always extenuating circumstances where you may need to break the law and drive above the speed limit. Self-driving cars will need some type of over-ride in these situations.

I would expect any self driving car would have a manual override. That would make it very possible.

At this time, there are too few electric vehicles on the road to bring in this technology.
They need at least 70% penetration of the total car market before introducing these restrictions, otherwise consumers will be put off from buying electric vehicles.
Once they realise that the whole vehicle can be governed from a central source.

Yes. Because sometimes (during road construction, for example) speed limits are temporarily reduced. So a road that used to have a limit of 45 MPH might now be set at 25 MPH.

Yes. some are really fast.

Self-driving car, maybe, but I own an electric car and there is nothing to prevent me from speeding, nor on any electric car that I'm aware of, and I've test driven all of them currently on the market.