Poor management decisions have been blamed for border control problems at Heathrow.
John Vine, the independent chief inspector of borders and immigration, criticised the implementation of organisational changes during one of Heathrow terminal three's busiest periods in a report published today.
He found that the introduction of team-based working, a new shift working system and the merging of immigration and customs roles had all "suffered from a lack of effective planning".
"This was far too much organisational change during Heathrow's busiest time of the year," Mr Vine said.
"I remain concerned that this lack of planning has affected the agency's ability to maintain an effective and efficient border control."
Passengers have been complaining of delays of up to three hours in getting through border control at Heathrow airport.
The report also found that two-thirds of 'examination of person' searches were judged to be neither justified nor proportionate.
A significant reduction in 'absconder recovery rates' was also noted.
But immigration minister Damian Green said the inspection on which the report was based had taken place before the Border Force was split from the UK Border Agency.
That represented another major upheaval for border control staff, caused by the row over border controls which nearly cost home secretary Theresa May her job last autumn.
Mr Green said action had been taken to tackle long queues since last November.
"We now have more staff at the border during peak times, greater flexibility to man immigration and customs controls, clearer guidance for staff on when vital checks are required and a national training programme with more emphasis on mentoring," he said.
"A culture change is underway to make Border Force an organisation that effectively tackles illegal immigration, protects the UK from terrorism and detects crimes like drug trafficking and weapon smuggling."
Shadow home secretary Yvette Cooper said the report was "extremely damning", however.
"People will be flabbergasted at Damian Green's complacency," she commented.
"His claim that the government has taken action since September to sort out these problems is flatly contradicted by the facts. Queues have got worse and worse.
"This government is spectacularly failing on immigration control, making families returning home wait for hours, yet stopping fewer people who shouldn't be entering out country from coming through."
Border control staff numbers at terminal three desks have dropped by 15% as a result of Home Office cuts, even though passenger numbers have increased. The terminal is Heathrow's second busiest and handles 20.4 million passengers a year.