As many as 30,000 UK passport applications have been affected by delays, David Cameron has said.
The Prime Minister insisted that hundreds of extra staff have been drafted in and new offices are being opened in Liverpool next week in to help tackle the backlog.
Ed Miliband called on Mr Cameron to “get a grip” as he warned that thousands of people face cancelled holidays as a result of the problems.
But Mr Cameron accused the Labour leader of trying to “frighten people”.
He said: “We have 300,000 extra applications than is normal at this time of year. We have increased massively the staff. The level of applications outside the normal three-week limit is less than 10% of that 300,000.”
Unions have claimed more than 500,000 applications are waiting to be dealt with and say delays in the service are down to the loss of 300 jobs and the closure of 20 passport offices over the past five years.
Photographs taken by anonymous members of the passport agency’s staff have emerged that are claimed to show boxes of passport applications stacked up and waiting to be dealt with in the Liverpool office.