William G. Sims

WILLIAM SIMS advises a range of global financial institutions on UK and EU financial services regulatory matters.

Bill trained and qualified as a solicitor in Sidley’s office in London, where he gained experience in the firm’s Global Finance; Restructuring; Banking, Payments and Fintech; and Labor, Employment and Immigration teams.

Bill’s recent experience includes assisting:

• A client with preparing regulatory compliance documentation for an application for FCA authorization as a payment institution.
• A U.S. bank with a cross-border corporate card issuance project.
• Various clients across the financial services sector to address legal and regulatory compliance queries relating to UK and EU legislation and regulatory frameworks.
• A U.S. insurance company with drafting and reviewing ISDA and regulatory initial margin documentation.

Bill maintains an active pro bono practice and undertook a three-month pro bono secondment to UNICEF UK in 2025 as part of Sidley’s post-qualification Pro Bono Fellowship, where he worked with the charity’s legal and fundraising regulatory compliance teams. He has also assisted pro bono clients with various matters including a Personal Independence Payment appeal, a British citizenship application, and wage/discrimination claims in the Employment Tribunal.