It is not explicit that all new suppliers are pre-assessed.
pg. 6
"Supplier selection
It is important that we only work with suppliers who share our values and vision, particularly on issues as important as human rights and modern slavery. Our Supplier Code of Conduct, as detailed above in the policies section, sets out the standards, ethics, rights and responsibilities that govern the relationships our business has with its value chain partners. We hold regular discussions with material key suppliers about working standards within the value chain and, after onboarding, continue to work with each supplier to drive improvement within the business.
We are further enhancing our due diligence during the sourcing process to ensure that we appropriately test, measure and score suppliers bidding for new business to ensure we only select those aligned with our values."