If it is a company that is applying on the life of a key person, then you simply put the company's details in the section 'About the other applicant' on page 3 and then put the details of the person covered on the following pages.
If it is a partnership and the key person is a partner, this would normally be arranged by the partner taking out the plan on their own life and putting this under trust for the benefit of the other partners. You would therefore leave the section 'About the other applicant' blank and complete the rest of the form in the normal way. It is however important to make sure we receive the trust form before the plan starts.