Home Secretary Theresa May has apologised for delays in processing passport applications and insisted the government is doing all it can to deal with the situation.
"I am sorry and the government is sorry," she told MPs in a Labour-led Commons debate on the delays.
There had been unusually high demand for passports, she said.
Shadow home secretary Yvette Cooper said the situation was a "shambles" and accused Mrs May of incompetence.
"She has come to this late. She hasn't had her eye on the ball," Ms Cooper told Parliament.
"It is really unfair on people who have saved up everything for their holiday and now it's being wrecked by her incompetence."
Mrs May said the passport office was dealing with the highest demand for passports for 12 years. She said the annual surge in demand in summer had started much earlier than usual.
Passport crisis in numbers
- Outstanding passport applications: 493,289
- Outstanding passport applications at this time last year: 146,939
- The backlog is 346,350 higher than it was 12 months ago
- Passport Office chief executive Paul Pugh says 90% of applications are being processed within the three week limit
- That means 34,635 people are facing delays
- In 2013, Mr Pugh predicted staff at UK Passport Offices would have to deal with an extra 350,000 applications this year as a result of the closure of seven passport centres in British embassies.
- He says the actual figure will be closer to 400,000 "over 12 months".
"I would like to say to anybody who is unable to travel because of a delay in processing their passport application that I am sorry and the government is sorry for the inconvenience they have suffered and we are doing all we can to put things right," she said.
Despite some lengthy delays, the majority of applicants are still receiving their passports within three weeks as usual, Mrs May said.
Over the first five months of the year, more than 99% of those making "straightforward" applications had received their documents within four weeks, she added.
The government has promised to "fast-track" delayed applications free of charge for those in urgent need because of imminent travel plans.
Mrs May said: "To qualify, they must have booked to travel in the next seven days, and they will need to provide proof of their travel plans.
"The upgrade will be available until further notice, and I can tell the House that since its introduction, 800 customers have used it to ensure that they receive their passports."
The debate had been opened by Labour's Ms Cooper, who said it was not clear what a "straightforward" application was.
The definition may exclude cases of parents applying for children's passports, which was where much of the problem lay, she continued.
"We still don't know when things will be back to normal, families still don't know how long they can expect to wait and we still don't know whether the Home Office has a grip," Ms Cooper said.
A helpline system introduced to help deal with the delays seemed merely to be taking messages and not responding, she claimed.
"We need the staff in place to clear the passports and make sure that constituents across the country are told what is going on," Ms Cooper said.
Labour MP George Mudie urged the Home Office to provide compensation for those who have lost out financially as a result of delayed passport applications.
Another Labour MP, Meg Hillier, who is also a former passports minister, said the problems should have been foreseen, and described the government's solutions as a "sticking plaster".