Holidaymakers who need to urgently renew their passports face missing their trips after Home Office systems went down.
The fast-track system allows people to book appointments for a new passport as early as two days after they apply and receive their new document within four hours of their appointment.
But staff told those waiting that they may need to reschedule as there was a “national system outage” and they did not know when it would be back up.
People were being encouraged to rebook another appointment, despite paying £239.50 to use the fast-track service - more than twice the £102 regular adult passport fee.
A Home Office spokesman said the issue has now been resolved and services are now operating as normal.
It comes less than two weeks after fast-track passport applicants were told their appointments had to be rescheduled when offices were closed due to “extreme weather”.
“Due to the extreme weather, London Passport Office will be closed on June 26,” the HM Passport Office told customers in an email at the end of June.
“Your appointment booking has therefore been rescheduled.
“You will have received an email with your new appointment. If the new booking date/time is unsuitable, please use the link in your confirmation email to cancel or change your appointment.
“We apologise for the inconvenience caused.”