Unfortunately adding an additional driver is not a feature we currently have. Since we changed our insurance policy back in February we have been able to really focus on changing local mobility. This is being achieved by being able to offer micro trips, starting from just 1 hour in length to run errands or see friends.
Currently over 50% of our bookings are under 1 day long which means the need for an additional driver is not as strong as it used to be. We do not want to compete with the traditional car rental where additional drivers is very much needed on long road trips around the UK.
That said, we will always listen to our members and if the demand for this feature grows then we will of course put a case together and work with our insurer to deliver on it. Do let us know if it is a deal breaker for you.