The BoE, along with regulators in Europe and the United States, is worried about the reliance of banks on a handful of Big Tech firms for cloud computing in increasingly critical banking services, and the impact an outage at one of them could have on financial stability.

"This is a big topic both within the UK and internationally," Victoria Saporta, BoE executive director for prudential supervision, told an event held by the Institute of International Finance, a global banking industry body.

A global approach would be best, she said.

"Our current thinking is that the most effective ... approach to managing these risks from critical third party services providers is through a combination of minimum resilience standards aimed directly at critical third parties ... coupled with resilience testing of these critical third parties," Saporta said.

(Reporting by Huw Jones; Editing by Edmund Blair)