By default, when you create a new admin, they have access to employee payslips and P60s. If you don't want an admin to have access to view other employee's payslips, it is easy to disable.
Click on your name or email address in the top-right hand corner, then click Settings.
On the settings menu, click Permissions, then click Admin.
On this page is listed all the current employees with admin rights.
Next to the relevant user, under View Employee's Payslips & tax documents, deselect the check box.
📎NOTE: An admin can only control this access if the main admin enables Manage access to payslips & tax documents to other admins.