No. Because we won't be able to track your mileage while you use other cars, you'll only be insured to drive the car noted on your Policy Schedule.
If you want to drive someone else's car temporarily, you'll need to be covered under another insurance policy from elsewhere.
There are many providers of temporary insurance if you need it.
We can't make any recommendations, and you should do your own research to find the best policy. To help you on your way, you could look at Cuvva (mobile app based) or Sky Insurance (web based). If you have an iPhone, we've also negotiated a 10% discount on temporary insurance from our friends at Lenny - use code BYMILES10.
It's worth noting that while some policies include cover for driving other cars, it's usually on a third-party only basis that's designed for emergencies.