David Cameron has accused Ed Miliband of frightening holidaymakers as he blamed any delays in the issuing of passports on the fact that the Passport Office was facing 300,000 more applications, which was "above normal".
Cameron said that "the Home Office has been on this from the very start", but Miliband said the prime minister needed to get a grip and demanded to know when the backlog will be cleared.
Miliband said: "Tens of thousands of people are finding their holidays are being cancelled because they are not actually getting a passport."
He demanded to know why British citizens were being told that if they wanted to have their passport within the three-week target, they needed to pay £65 extra.
Downing Street said hundreds of extra staff had been deployed and offices would open seven days a week from 7am until midnight, after leaked photographs showed boxes of applications piling up in temporary storage.
Families should not face delays in the runup to the holiday season and the government would have to remain "vigilant" following the highest level of applications in 12 years, Cameron's official spokesman said.
The government has finally admitted there is a problem despite denials in previous days from the Passport Office that they are having to clear a backlog.
It comes after MPs said they had been inundated with complaints and the PCS union said the Passport Office was in crisis.
In the Commons, Cameron said: "We have increased massively the staff and the level of applications outside the normal three-week waiting period is less than 10% of the 300,000 additional applications."
He insisted: "The government has taken action to deal with this problem not today but in weeks gone past. We have 250 staff already redeployed to the frontline, prioritising all outstanding applications allowing for an extra 25,000 examinations weekly."
In addition, the Passport Office was now working seven days a week with 650 extra staff on the helplines to support customers.
Theresa May, the home secretary, also announced a new office will open in Liverpool next week with 100 additional staff.
Miliband demanded to know at what point the government became aware of the problem, and said May had been distracted by her fights with the education secretary. Cameron countered: "I hope he will be careful not to try and frighten people in the way that he did."
May said the problem was caused by a "very, very high" level of applications at the beginning of 2014.
She said: "We will continue to look at this issue and the Passport Office will put more staff in place and resources in place to ensure they can deal with these applications."
Cameron's spokesman said the prime minister "very much understands concerns about the delays that people have been experiencing".
"That is why it is absolutely right that additional measures have been taken," the spokesman said.
"We will continue to stay very vigilant on this, because families shouldn't face delays."
Earlier, James Brokenshire, a Home Office minister, acknowledged that Passport Office workers were dealing with the unexpected strain of 460,000 forms.
He denied there was a backlog of "straightforward" cases but did not address the issue of whether more complex cases were piling up.
The photographs were leaked to the Guardian after the Passport Office denied claims by the PCS union that it was in a crisis worsened by job cuts and office closures.
Speaking on BBC Radio 4's Today programme, Brokenshire said: "I do accept that there has been the additional pressure that's been brought to bear.
"The Passport Office's figures for performance are showing that for those straightforward cases of renewals, child applications, that they're turning those around at around 97% in three weeks, 99% in four weeks. But I understand we're not just talking about numbers here. We're talking about people, we're talking about holidays and therefore our focus is supporting the Passport Office on the additional resources they've put in.
"They've redeployed people, they're now working seven days a week, extra hours as well, and there are further steps they're taking in addition because we recognise that getting passports turned around efficiently and effectively matters to people."
Mike Jones, of the PCS union, told the Today programme: "The reality is, for your listeners, that they recognise that there is a backlog, because when they expect to get their passports within three weeks and we're getting thousands upon thousands upon thousands of examples whereby … it has taken nearly two months or more for people to get the passports, that clearly is a backlog."
Paul Pugh, the interim chief executive of the Passport Office, has maintained that there is no backlog of passports.
He said: "We have been experiencing exceptional early summer demand for passports, in part due to the improving economy and a rise in holiday bookings.
"During this busy period we have processed more than 97% of straightforward passport renewal and child applications within the three-week target turnaround time.
"There is no backlog – over 99% of straightforward applications have been processed within four weeks."
The home affairs select committee has asked Pugh to give evidence on the delays next week.
David Hanson, the shadow immigration minister, said the photographs would confirm the suspicions of many people who have tried to deal with the office in recent weeks, and called on May to get a grip of the problem.
"Every picture tells a story and it is clear from constituency contact that passport cases are piling up across the country. The home secretary won't even admit there is a problem, let alone take action to deal with it.
"Even according to the government's own statistics, 90,000 passport cases haven't been dealt with on time this year, so there is simply overwhelming evidence that families across the country are suffering needless stress, anxiety and problems simply because of mismanagement at the Home Offfice."
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