More than 40 embassies, consulates and High Commissions in the United Kingdom have been told by HSBC to close their accounts with the bank within 60 days.
Part of a programme to reduce business risks, the move has created "havoc" as diplomats are scrambling to open new accounts with other banks, the head of the UK's Consular Corps told the Mail on Sunday.
The Vatican's ambassadorial office in Britain, the Apostolic Nunciature, are among those said to be affected.
HSBC said embassies were subject to the same assessments as its other business customers. They need to satisfy five criteria - international connectivity, economic development, profitability, cost efficiency and liquidity.
"HSBC has been applying a rolling programme of "five filter" assessments to all its businesses since May 2011, and our services for embassies are no exception," states an HSBC spokesman. "We do not comment on individual customer relationships."
Vatican's ambassadorial office in Britain, the High Commission of Papua New Guinea and the Honorary Consulate of Benin are among those said to be affected.
"We've been banking with HSBC for 22 years and for them to throw us off in this way was a bombshell," John Belavu, minister at the Papua New Guinea High Commission, told the paper.
Lawrence Landau, honorary consul of Benin, told the Mail his mission had been having trouble finding a new bank.