Britain's Financial Services Authority said it had fined Ian Hannam, JP Morgan's Global Chairman of Equity Capital Markets and one of London's best-known and most colorful investment bankers, 450,000 pounds ($720,700) over the breach.
JP Morgan announced Hannam's resignation to staff in a morning memo minutes afterwards.
Hannam, an industry veteran whose current deals include advising miner Xstrata (XTA.L) on its merger with Glencore (GLEN.L), said he had fully cooperated with the FSA and would appeal against the decision.
"I will complete my current client commitments and ensure a smooth handover of responsibilities," Hannam said in an emailed statement. "Appealing the case while still at the firm would be an unfair distraction to my clients and colleagues."
The FSA said in its statement that Hannam had disclosed insider information on Heritage, a JP Morgan client, in two emails sent to a prospective client in September and October 2008. One email contained information about a potential offer for Heritage, while another detailed a new oil find.
Hannam is known for his role in the tie-up between blue-blood advisor Cazenove and U.S. rival JP Morgan, and for his work with some of the top players in the mining sector, including Xstrata.
Major deals outside the mining sector include the merger between Virgin Media and NTL and the creation of SABMiller.
A former soldier and engineer who began his career with house builder Taylor Woodrow, South London-born Hannam started his banking career in Salomon Brothers in New York in the early 1980s before moving to Robert Fleming in 1992.
Heritage Oil declined to comment. ($1 = 0.6244 British pounds)
(Reporting by Sudip Kar-Gupta, Douwe Miedema, Victoria Howley and Clara Ferreira-Marques; Editing by Douwe Miedema)
Reuters