More than 1,000 members of the Public and Commercial Services union (PCS) at eight sites are walking out in an escalation of the long-running row.

Picket lines will be mounted on Monday outside the offices in Glasgow, Durham, Liverpool, Southport, Peterborough, London, Belfast and Newport in Wales.

The union said those taking action will be supported by a strike fund.

PCS general secretary Mark Serwotka has written to the government calling for urgent talks in a bid to resolve the dispute.

He has accused ministers of treating its own employees differently to others in the public sector after negotiations were held with unions representing health workers and teachers.

The union is stepping up strikes, with a nationwide walkout of more than 130,000 civil servants planned for April 28.

The Home Office said the Passport Office has already processed more than 2.7 million applications this year, adding over 99.7% of standard applications are being processed within 10 weeks, with the majority of those delivered to customers well under this timescale.

There are currently no plans to change official guidance which states that it takes up to 10 weeks to get a passport.