Rac Car Insurance

Can I legally drive if I have two insurance policies on one car?
Today I have just been insured on my mums car. She took out a new policy as the exisiting policy wouldn’t allow me to join. We are gonna cancel the first policy, but it was to late as their phone lines are closed, also the company (RAC insurance) is closed on Sunday, so that has to be done on Monday. Can I drive my mums car tomorrow and is it legal.
Yes. Even if you had an accident in the mean time only ONE company would cover the claim.
