If you don't have acceptable proof, you can still keep the policy, but you'll need to reduce your NCD to 0 years and this will increase your premium.
To reduce your NCD you just need to:
You can reduce your NCD, see how it'll affect your premium and make any extra payments.
If your policy hasn't started yet, you'll need to set the 'effective date of change' to be the same as your start date.
If you don't want to keep your policy without the NCD, you can cancel the policy.
You can find out how to do that view our FAQ on how do I cancel my car insurance policy?