The company has mentioned reviewing the suppliers however does not explicitly state audits or onsite visits.
pg. 2
"We take a risk-based approach and consider the risk of modern slavery and human trafficking occurring within our supply chain to be low. Nevertheless, we continue to seek ways to earn and maintain the trust and loyalty of our partners and clients by adhering to the highest standards of ethical behaviour and fiduciary responsibility. In early 2021, we re-assessed the modern slavery risks in our supply chain which included a review of services and goods being acquired by BlackRock UK. For those goods/services that are at a high(er) risk for modern slavery, including underpayment or exploitation of vulnerable workers, we’ve identified the current suppliers and have asked them to complete a due diligence questionnaire via our ‘Know Your Third Party’ (KY3P) tool A similar due diligence review will be conducted on any new suppliers prior to providing higher risk goods or services, as well as a periodic review on existing suppliers."