A union has warned of industrial action over a passport backlog it says has been caused by job cuts.

The Public and Commercial Services union said job cuts over the past five years had led to a "crisis", with long delays dealing with applications.

The union said over 300 jobs had been lost in recent years and over 20 offices had closed.

Staff were trying to deal with a backlog of almost half a million cases, said the PCS.

The union has warned it will consider industrial action if the issue is not tackled by the end of the month.

General secretary Mark Serwotka said: "The passport office is failing holidaymakers because of a political decision to cut staff and close local offices.

"While the economy is showing signs of recovery for some, the damage being done by the Government's spending cuts is evident to anyone trying to get a passport at the moment and we are not prepared to stand by and allow this to happen."

Chief executive of Her Majesty's Passport Office, Paul Pugh said:"We have been experiencing exceptional early summer demand for passports, which seems to be in part due to the improving economy and a rise in holiday bookings.

"Staff were brought in immediately to respond to the extra demand. We are operating seven days a week and our couriers are delivering passports within 24 hours of being produced.

"We have issued almost three million passports for UK customers in 2014, including over one million issued in the eight weeks since the start of April.

"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, with over 99% of straightforward applications being processed within four weeks.

"We would remind people of our existing advice to customers: allow plenty of time when applying for a new or renewed passport as a passport will not be issued until the necessary security checks have been done, and do not book travel until you have received your passport."

Labour MP Katy Clark (North Ayrshire and Arran) said there were "severe delays" in her constituency, with increasing numbers of complaints that people were not receiving their passports before they were due to travel.

She said: "In the past few weeks my office has seen a surge in constituents seeking help with their passport applications.

"It is clear there are significant delays and a backlog of applications within the Passport Office, which management are failing to address.

"The delays and backlogs are the product of significant cuts and reductions to the Passport Office."