They were envisioned as low-key, across-the-pond fund-raisers that would allow Mitt Romney to extract campaign cash from expatriates in London by night as he played statesman by day.

But the two receptions that Mr. Romney, the presumptive Republican nominee, will hold for donors next week during a swing through Europe are turning into an ill-timed public relations headache for him.

Several of the events’ hosts are top executives at banks tied to the interest rate-fixing scandal that is now engulfing London’s financial and political world, linking Mr. Romney, however superficially, to a messy moment in the continuing debate over Wall Street excesses.

The British and American authorities are examining the role of more than 10 banks in the possible manipulation of key interest rates that affected how consumers and companies borrowed money around the world.