Late last year, the JPMorgan chief executive, Jamie Dimon, called Britain’s chancellor of the Exchequer, Alistair Darling, to voice his displeasure over the tax  the only head of an American bank to make such a call, people at the British Treasury said.

Image Late last year, the JPMorgan chief executive Jamie Dimon voiced his displeasure over Britain’s 50 percent tax on bonuses paid by financial institutions to many of their employees. Credit... Ramin Talaie/Bloomberg

During the conversation, Mr. Dimon said that JPMorgan, which employs 15,000 people in Britain, was not just a significant taxpayer but was also making a $2.4 billion investment in Canary Wharf and that it had not taken a penny of government aid.

The conversation was first reported by The Daily Telegraph and received considerable attention in London, with some arguing that it was an early indicator that increasing regulation was going to induce banks to take their business elsewhere  to Geneva, New York, Frankfurt or Singapore.

But the situation is far more complicated than that.

A person who was briefed on the conversation said that while it was true that JPMorgan, as with most banks, was furious over the tax, the conversation between Mr. Dimon and Mr. Darling was civil and did not represent a threat that the bank would pull back from its Canary Wharf project.

In fact, there were other reasons before the tax was announced that made the building project less than attractive for the bank  namely that the bank had laid off thousands of employees since the project was conceived in 2008 and no longer needed such a large space.

Still, even if unspoken, the message behind the call was clear: There is a limit to what banks will accept as the price of doing business in Europe’s premier financial center.

To be sure, bankers are often noted to be the best of blusterers. It is one thing for a strategy committee to study the feasibility of moving part of a bank’s business to an alternative locale, as Goldman Sachs has done. It is quite another matter  logistically and financially as well as culturally  to move, say, 2,000 bankers and operations staff members to another European city, no matter how appealing it might be for their bonus pay.