Most policies will include details of what is covered in this situation. An example of the policy wording is as follows:
Your policy will not make any payment for any event that is more specifically covered by another insurance policy and will only pay a proportionate amount of a claim where there is other insurance in force (such as Home Contents and All Risk insurance policies) covering the same risk, and we will require you to provide details of such other insurance.
If this is applicable to you, please check your policy wording.