Walkers will not have to provide contact details so there is no danger of people incriminating themselves. In addition, the MCofS, which will collect and collate the data, is not subject to Freedom of Information requests and any personal data would also be protected under the Data Protection Act.
The form can be accessed here and needs to be completed and returned by 30 June. The MCofS is interested in both recent and past crossings of the line so please have a think about the times you have climbed Ben Lui and complete the form if your route included the railway line.