A US Congressional report revealed UK officials, including Chancellor George Osborne, added to pressure by warning the US it could lead to market turmoil.
The report alleges the UK "hampered" the probe and "influenced" the outcome.
HSBC was accused of letting drug cartels use US banks to launder funds.
The bank, which has its headquarters in London, paid a $1.92bn (£1.48bn) settlement but did not face criminal charges. No top officials at HSBC faced any charges.
'Serious implications'
The report says: "George Osborne, Chancellor of the Exchequer, the UK's chief financial minister, intervened in the HSBC matter by sending a letter to Federal Reserve Chairman Ben Bernanke... to express the UK's concerns regarding US enforcement actions against British banks."
The letter said that prosecuting HSBC could have "very serious implications for financial and economic stability, particularly in Europe and Asia".