The Passport Office has denied that it is failing to cope with applications, despite claims of severe delays.
Chief executive Paul Pugh said more than 99% of “straightforward applications” were being processed within four weeks.
His comments, reported by the BBC, follow earlier denials by home secretary Theresa May and the Home Office of major problems in the system.
The Commercial and Public Services Union has said it believes there are 500,000 applications currently in the system but it does not know how many have been delayed.
It has claimed the loss of a tenth of the agency’s workforce in the past five years and the closure of local passport offices has contributed to “major problems”.
Assurances that there is no backlog were challenged by leaked photographs revealing piled up boxes of hundreds of files of applications stacked in a Liverpool passport office room usually used for meetings, the Times reported.
Pugh has been asked to appear next week before the Commons home affairs select committee.
The Passport Office boss said there had been “exceptional” summer demand but that extra staff have been brought in to handle applications.
“We are operating seven days a week and our couriers are delivering passports within 24 hours of being produced,” he said.
“We have issued almost three million passports for UK customers in 2014, including over one million issued in the eight weeks since the start of April.
“During this busy period we have processed more than 97% of straightforward passport renewal and child applications within the three week target turnaround time.”
May told the Commons yesterday of an “unprecedented” demand for passports earlier this year.
But the Passport Office had still managed to achieve its customer service targets, she said.
Shadow home secretary Yvette Cooper said MPs from all sides of the house had been contacted by constituents worried about their applications.