In what amounts to the start of a new trade war between the UK and Argentina, the banks - understood to include the Royal Bank of Scotland, Barclays Capital and Goldman Sachs - have been warned they face criminal and civil action in the Argentine courts.
The threats were made in a series of letters sent to as many as 15 banks by the Argentine embassy in London over the last ten days.
The letter, a copy of which has been seen by The Sunday Telegraph, warns the institutions that even merely writing research notes on exploration companies involved in the Falklands constitutes “a violation of the applicable domestic and international rules”.
The news - coming a day ahead of the 30th anniversary of Argentina’s invasion of the Falklands which sparked the 1982 conflict - is likely to worsen tensions between the two countries. The Argentine government is continuing to push for sovereignty.
The two-page letter, to which a schedule of legal declarations about the Falkland’s ownership are attached, is intended to warn off the banks from any further involvement in the South Atlantic oil industry.