I've not found ANY Commercial Policy that would left you drive another car - that would be like gaining a Pilots Licence and assuming you were covered to fly a Helicopter ! I have a Classic Policy for my Capri that only covers me to drive the one car with limited mileage - a standard car policy that lets me drive any other CAR, (not vehicle), that's not mine with 3rd Party only cover and a Commercial Policy from Flux that covers myself only to drive my truck. The last one doesn't even cover me to drive another van or truck and I've not yet found a Commercial Policy that does. Assumption is a very, very risky thing to do with any insurance as had you not been a named driver you'd be looking at Court, an instant 6 points and a fine depending on your level of culpability - good save matey !