Is that you as a learner driver or full licensed driver named on the policy?
Is you dad using his no claims on his own policy? If he is, you cannot use the same no claims on another policy.
Also bear in mind, that by not declaring who is the main driver, you and your dad are committing fraud, which is illegal and can lead to you being disqualified from driving if you get 6 points on your license for being uninsured.