Long queues at the UK's busiest airport have been caused by a lack of effective planning amid job cuts inspectors said on Thursday.
Limited resources are not being matched to the demand at London's Heathrow Airport, damaging the ability of border staff to maintain effective and efficient controls, the chief inspector of borders and immigration John Vine said.
The introduction of a series of significant changes "was simply far too much organisational change during the busiest time of the year", Vine reported.
The critical report on the UK Border Agency (UKBA) and the Border Force comes as Heathrow faces another shake-up as Home Secretary Theresa May responds to the ongoing row over queues.
The introduction of new team structures, rosters and shift patterns came as border staff numbers at Terminal 3 fell by 15% from 322 to 277 in the 12 months to last August, inspectors said.
A new team-based working, designed to ensure staff work in the same teams each day, was blaming, for it brought a lack of flexibility, with low staffing numbers when passengers numbers were high but high staffing levels during quieter periods.
The report found that queue targets for passengers from outside the European Economic Area (EEA) were breached 62 times between September 18 and 30 last year, with the longest wait hitting two hours and 15 minutes.
On 27 September, the queue target was breached for seven consecutive hours.
The inspectors also raised serious concerns over the use of eGates, which use facial recognition technology, and called for the Border Force to investigate whether they provide adequate security.
The report found that the two officers who were needed to operate the gates could process more people manually at desks.
In one 15-minute period, two staff on desks processed 66 passengers while just 22 went through the two eGates.
Immigration Minister Damian Green said of the report that: "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.
"A culture change is under way 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 responded to the report by saying that: "This is an extremely damning report on Government mis-management of our border security.
"It makes clear that the Home Secretary's decision to cut so many staff is having a serious impact, with for example a 15% drop in border staff at desks at Terminal 3 even though passenger numbers have increased."Suggest a correction