Advise the insurer.
Failure to do so may result in the insurers declining a claim on the basis of you not notifying them of a ‘material fact.’
It is not relevant whether they charge an additional premium, other than you would need to pay the additional premium. The important element is to advise them.
Your worse case for non-disclosure is the insurer voiding the policy from inception, at which point the police become interested in your activity of riding on the public highway during for the last ‘X’ period without insurance.