Packages containing a caustic substance disguised as eucalyptus oil were sent to Prime Minister Tony Blair and a Scottish legislator, Scotland Yard said.
No injuries were reported, but police issued a warning saying similar packages may have been mailed. Blair was visiting Australia to attend a Commonwealth summit. The Scottish legislator was not identified.
Scotland Yard said it was alerted to the packages in an anonymous telephone call from a man who claimed to have sent 16 of them. Authorities said the caller claimed to be a member of the Scottish National Liberation Army, a separatist group.
Forensic tests showed that the substance was sodium hydroxide, a corrosive chemical that can cause damage to skin and tissue.