From the article:
“Documents from Britain’s national archives showed that Nathan Mayer Rothschild had allowed the use of slaves as collateral in banking dealings with a slave owner, while Freshfields’ founding partner James William Freshfield acted as a trustee in deals involving Caribbean slave plantations, the FT reported. Freshfields said it had not been aware of the documents, which academics at University College London are studying.”
ETA (Financial Times): British Companies Express Regret for Slavery Connections