The chance of airport security queues of up to four hours cannot be ruled out during the London Olympics, the director general of the UK Border Force said today.
Brian Moore said he was satisfied that planned staffing levels were adequate to deal with the expected surge of arrivals, but said he could not guarantee there would be no delays.
"I do not anticipate seeing large queues of two, three and four hours because of the work we are doing to move our resources," he told MPs when pressed about recent problems.
"However there will always be circumstances beyond our control."
He repeatedly declined to tell the Commons home affairs committee what he personally considered a "reasonable" wait, but said he believed the public generally accepted a 25-minute target.
"Most people find that 25-minute mark to be not unreasonable," he said, but that did not mean that longer delays were necessarily unreasonable.
He conceded that the flexible deployment of resources was "sometimes not a strength of the Border Force" but that effective actions were being taken to deal with recent issues.
Mr Moore denied contingency staff being drafted in to man border posts over the summer were receiving less training than permanent colleagues.
The five or six-day procedure is the equivalent of the period within the standard 15-week training that relates to the particular part of the role they are carrying out, he said.
"It is a different role. We have given them an adequate amount of training."
But he conceded his staff were "feeling the pressure" of the squeeze on public spending.
"Everybody in the public sector is feeling the pressure. There is no question about that and so are my people," he said, saying they were looking for "continuity and stability".
Asked about poor morale, he said that like any organisation there were "some at the back who, no matter what happens, will never be happy".
Asked if he was seeking to remove those, he said he would "make sure everybody knows what it expected of them".
He played down reports that Prime Minister David Cameron was personally unhappy at the performance of the Border Force, of which Mr Moore took charge in March.
"I perhaps don't always accept everything I read in the press," he said.