You do not have to comply with vexatious requests. There is also no requirement for you to carry out a public interest test or to confirm or deny whether you hold the requested information.
In most circumstances you must still issue a refusal notice within 20 working days. This should state that you are relying on section 14(1) and include details of your internal review procedures and the right to appeal to the ICO.
There is no obligation to explain why the request is vexatious. The code of practice issued by the Cabinet Office under section 45 states that when refusing a request under s14(1), a public authority is not required to explain why the request is vexatious, but comments that a public authority may wish to do so as part of its duty under section 16. Therefore, although you are not legally obliged to provide advice and assistance where a request is vexatious, you may choose to do so and should aim to be as helpful as is practical.
Where you have not been able to identify a value or serious purpose to the request, explaining this will provide the requester with the opportunity to provide more details that you can consider at internal review. We consider it good practice to include the reasoning for your decision in your refusal notice.
However, we appreciate that it may not be appropriate to provide a full explanation in every case. For example, if the evidence of the requester’s past behaviour suggests that a detailed response would only serve to encourage follow-up requests or correspondence.
Therefore, the question of what level of detail, if any, to include in a refusal notice depends on the specific circumstances surrounding the request.