What you need to do
The overall scope will have been defined at high level in the Outline Business Case. It now needs to be defined in detail taking into account the business requirements. This will set the bounds to the requirement and includes:
What the core requirement is to cover
What related work is to be excluded e.g. to be retained in-house or provided by another contract
What is optional: related work that whilst not essential in meeting the business objectives of the procurement could beneficially be provided by the supplier.