Does my Motability Insurance (RSA) cover me to drive another vehicle with owners consent

No. You can only drive the motability car with this type of insurance. You cannot drive any other car whether it's your friends or family with or without their consent. Your insurance covers only your vehicle and nothing else.

You are allowed though to drive a car that's been provided by or on behalf of Motability Operations as a replacement for your current one.

Source : http://www.motability.rsagroup.co.uk/

No you can't as this is against the policy