Insurance....driving other cars?

I was stopped last year driving my brothers car. My policy covers me to drive any other vehicle 3rd party. As it turned out my brothers insurance had expired the previous month (he's never been good at this sort of thing )

I got a producer so phoned my mates who's a copper to see where I stood, he said the other vehicle does not have to have insurance and fortunately this was born out at the local police HQ when I produced the insurance for my car only.