This issue has come before the financial ombudsman in relation to a claim refused by an insurance company.
In this case, the insurance company refused to pay out because the holiday was due to be taken after the expiry date of the annual insurance.
The ombudsman held that the insurance company was liable for the claim, otherwise as in your position you would need to take out an additional annual insurance policy while the current policy was valid.
Therefore you only need to ensure you have another annual policy in place from the date of expiry of the current policy.