Up to 30,000 passport applications have been hit 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 the premier 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."