The boss of Eurostar has told Sky News that congestion warnings for London ahead of the Olympic Games put tourists off travelling to the capital.
Nicolas Petrovic was speaking after the company, which was among the Olympics' sponsors, confirmed a boost from the Games.
The channel tunnel firm carried 4% more passengers at the time compared to the same period last year.
Eurostar said 2.6 million people used the service between July and September 2012, but it was a flat performance as many UK travellers chose to stay at home to save money and watch the Olympics.
There were also fewer business travellers than usual, the company said.
Mr Petrovic said: "What we didn't see coming was that in July the leisure passenger, the tourist, didn't come to London.
"Also the business market went down much earlier than usual because of all the calls to avoid London - [because of] the traffic here."
Sales revenue fell 5% this summer to £188m - down from £197m in July-September 2011.
Eurostar, which runs trains between London's St Pancras station and Paris and Brussels, said that since end of the Games it has seen growth in passenger numbers and sales revenue.
The recent increase signalled "a positive outlook" for the period October to December 2012, the company said.
Eurostar said is also continuing a £700m fleet investment programme to refurbish its trains and carriages in a bid to improve customer experience.