The Chief Inspector of Borders and Immigation has warned that border staff with only basic training - and little immigration experience - are being used to cut queues at Heathrow Airport during the Olympics.
John Vine says that extra staff, being drafted in to help during the busiest periods, also lack confidence and are taking more time to process passengers despite asking fewer questions.
Employees who have left their jobs, or retired, are also being re-hired by the Border Force, while other Home Office and UK Border Agency staff are being given training so that they can man the immigration desks.
In total, 500 extra staff will be deployed as the airport prepares to deal with more than 100,000 passengers a day during the busiest periods during the Games.
Shadow home secretary Yvette Cooper said: "The Olympic countdown has started yet the Home Secretary still hasn't sorted the chaos at our borders caused by her decision to cut so many staff this year.
"Re-employing former immigration staff, having cut nearly 900 people from the Border Force since the general election, is a damning self-admission of failure and a waste of taxpayer's money too."
But the Border Force insists that there have been "real improvements at Heathrow" since the April inspection.
A spokesman said: "John Vine acknowledges the positive addition of hundreds of extra staff deployed to meet demand, the creation of a central control room to manage resources and on-going recruitment of more border officers," she said.
"Border Force has already addressed concerns raised during the April inspection including staff being issued with the operating mandate to reinforce clear standards for carrying out border checks.
"We are also working with (airport operator) BAA on improving queue measurement, looking at securing staffing levels for the long-term and continued training and mentoring for contingency staff to ensure they carry out efficient and secure check on passengers."