A backlog of more than 400,000 passport applications has mounted due to disruption caused by the coronavirus pandemic, figures showed.
Home Office minister Baroness Williams said reduced staffing to allow social distancing meant forms were taking longer to process.
She said steps were being taken to increase capacity after travel restrictions were eased.
But those applying may have to wait longer than the usual three weeks.
In a written Parliamentary answer about the backlog, Baroness Williams said HM Passport Office “continues to operate at reduced staffing levels so its people can continue to socially distance”.
She added: “It is therefore taking longer than usual to process passport applications.
“As part of its contingency arrangements, HM Passport Office is rapidly increasing its capacity for processing passport applications, in line with public health guidance, which will help to ensure it continues to meet the travel needs of its customers.”
As of 7 July, she said, work was under way on about 126,000 passport applications – 31% higher than at the same period last year.
The minister pointed out a further 284,000 applications would “need to be worked through in the coming weeks once initial documentation has been received and allocated”.
This represented an increase of 172% from last year, she said.
Baroness Williams disclosed the scale of the passport backlog in a response to a question by Labour over the delays.
The relaxation of Foreign Office guidance on non-essential overseas travel and quarantine rules earlier this month has paved the way for foreign holidays to destinations including Spain, Germany, France and Italy.
Those applying for new passports will be among the first to receive a blue version, introduced from April after 30 years, following the UK’s departure from the European Union.