The Trustees produce a Statement of Investment Principles (SIP) for both the defined benefit (DB) and defined contribution (DC) sections of the scheme. These statements explain the Trustees' policy on investments, including the kind of investments the scheme will have, the reasons for the options available in the DC scheme, how risks are managed, and how the Trustees engage and vote as shareholders. You can read both SIPS here:
Statement of investment principles DB 2019
Statement of investment principles DC 2019