LONDON Britain's Financial Conduct Authority has asked 20 banks and other financial firms to check if they have any ties to Panama law firm Mossack Fonseca, the FCA said on Thursday.
A massive leak of documents from the law firm detailed how the world's rich skipped through loopholes to park cash in low-tax jurisdictions.
"We have written to the firms earlier this week," an FCA spokeswoman said.
HSBC, Britain's biggest bank, has dismissed suggestions it has actively used offshore structures to help clients cheat on their taxes.
The bank has said the documents from Panama pre-dated a thorough reform of its business model.
(Reporting by Huw Jones; editing by Jason Neely)