The backup at Heathrow Thursday night happened after some flights were delayed due to rain, creating an influx of international passengers to the under-staffed immigration check points once the planes landed, The Telegraph reported.
Passengers from the United Kingdom and European Union states passed through immigration within about an hour, but passengers from other countries had to wait up to 2 hours to get out of the airport.
"It is terrifying, when you think about the Olympics and the crowds, this was just a regular Thursday night with a bit of rain," said one passenger, whose name was not reported.
"They were clearly expecting this as they had set up all these extra barriers up and down the corridor. They knew this was happening," he said.
Heathrow's owner, British Airports Authority, called the long lines "unacceptable" and members of Parliament spoke out against the fiasco, the BBC reported.
"Immigration waiting times during peak periods at Heathrow recently have been unacceptable and we have called on the Home Office to address the problem as a matter of urgency," said a BAA spokeswoman. "There isn't a trade-off between strong border security and a good passenger experience -- the Home Office should be delivering both."
"Huge damage is done to our country's reputation," Vaz said. "The government has a choice either to increase the number of staff at the airports or to restart the suspension of the checks. This needs to be done irrespective of the Olympics. This is not an Olympics issue. It is about ensuring that Heathrow is a world-class airport every day of the year."
Border Force, the agency responsible for immigration checks at the airport, said, "We will not compromise border security but we always aim to keep disruption to a minimum by using our staff flexibly to meet demand."