Long queues at Heathrow, the UK's busiest airport, have been caused by a lack of effective planning amid job cuts, according to the chief inspector of borders and immigration.
John Vine says limited resources have not been matched to the demand at Heathrow, reducing the ability of border staff to maintain effective and efficient controls.
Two reports into the service at Heathrow Terminal 3 and Gatwick North discovered that staffing levels were cut at some peak periods, and increased during quieter times.
At Heathrow, where staff numbers were cut by 15% in the twelve months to last August, the report found new working patterns for staff suffered from a "lack of effective planning".
Even though the airport management raised concerns that staffing levels had been cut at busy times and increased at quieter times 10 days in advance, it was told that there was not enough time to change staff rotas.
Mr Vine said: "This was far too much organisational change during Heathrow's busiest time of the year.
"I remain concerned that this lack of planning has affected the agency's ability to maintain an effective and efficient border control."
The report follows growing criticism of the reorganisation of border staff, which has been blamed for queues of up to three hours in arrivals at some UK airports.
Damian Green , the immigration minister, said: "This report covers the period before the Border Force was split from the UK Border Agency and since then we have taken action to tackle these issues.
"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."
At Gatwick's North Terminal, inspectors found that while some officials enforced the law in seizing goods, others allowed passengers to retain excess amounts or even the total amounts carried without penalty.
The critical report also found detection officers were missing from the green channel for significant periods of the day, which "clearly impacted the capacity to maintain detection activity".
Unions representing border staff told Sky News they are not surprised by the findings, claiming problems with the new working practices are still continuing.
The deputy general secretary of the Immigration Services Union said: "The levels of staff sickness is highlighted in the report and it's in large part because of poor management and the impact of team working.
"It remains to be seen whether the partial changes that they've proposed are going to be sufficient to address that particularly as we come into such a busy time."