One of Britain's biggest trade unions on Wednesday warned that travellers face severe disruption after its members working in passport control at airports voted to strike over Christmas.

The general secretary of the Public and Commercial Services (PCS) union, Mark Serwotka, said Border Force guards would walk out on eight days from December 23 to 31.

Other PCS members working in other government departments, including the Highways Agency and the Department for Work and Pensions, have already announced walkouts over pay and conditions.

Serwotka said workers were struggling to cope with the soaring cost of living, caused by double-digit inflation and sky-high energy prices on the back of the war in Ukraine.

"The government can stop these strikes tomorrow if it puts money on the table," he said, telling a London news conference the walkout would have "severe" effects.

PCS members were "desperate" and a proposed 2% pay increase was not enough, he added, promising to escalate action in the new year unless the deadlock was broken.

The strikes are part of a spiralling number, including railway workers and nurses to ambulance drivers and teachers.

They will involve Border Force staff, employed by the Home Office to check passports, on December 23, 24, 25, 26, 28, 29, 30 and 31.

The PCS members set to take part work at Britain's busiest airports - London Heathrow and London Gatwick - as well as Birmingham, Cardiff, Manchester and Glasgow.

The seaport of Newhaven, in southeast England, will also be affected.

Prime Minister Rishi Sunak hit out earlier Wednesday at "unreasonable" union leaders and warned of "new tough laws" to protect the lives and livelihoods of the British public.

He did not elaborate but appeared to be referring to proposals first put forward in 2019 for a minimum level of service during strikes.

Sunak's spokesman later said work on the plan was taking place "at speed". "We will consider all ways of curbing further action including legislation," he told reporters.