The Passport Office is advising only people going away before September or those travelling on compassionate grounds should apply now for a passport.
This comes as a reduction in staff to ensure that after measures are in place due to coronavirus has now lead to a backlog of 400,000 passport applications new figures show.
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.
Therefore anyone wishes to book a holiday abroad this summer, may want to check their passport expiry date before booking.
She said the latest figures show that as of 7 July, 120,000 passport applications have begun being processed – 31% more than the same time last year
But there are still 284,000 to go – a spike of 172% compared to last year, she cautioned.
In-person interviews, usually needed for those trying to get their first adult passport or what to use the Fast Track system, are also “temporarily unavailable”, the website adds.