The tadpole configuration has stability issues though, rolling it over is fairly easy if the vehicle has a high center of gravity.
The Reliant Robin solved that for the most part by reversing the arrangement putting the single wheel in front, but they still tend to overturn quit easily.
The accident mentioned above during the demonstration probably really was caused by that other car, but the ease with which a three wheeled configuration turns over most likely contributed to the severity, and in the long run would have had to be solved using tricky engineering such as a single wheel for low speed maneuvering and two wheels for higher speeds.
Here is a Reliant Robin doing what it does best:
I think there is a topgear episode where they try to improve the Reliant Robin by putting training wheels on it.