Border Force officials will on Friday join the wave of industrial action across Britain, starting the first of a series of strikes at airports, while Royal Mail workers strike again for two days before Christmas. Passengers travelling into the UK have been warned to be prepared for longer queues at immigration in airports, while many letters and parcels will now go undelivered before Christmas, as staff take action over pay trailing behind inflation. Heathrow, the biggest of the six airports where Border Force staff are to strike, said it expected the vast majority of journeys to be unaffected, with no flights cancelled before the industrial action. About 1,000 members of the Public and Commercial Services (PCS) union will continue to strike over the remaining days of 2022, apart from 27 December. The Home Office, which is responsible for Border Force, has drafted in officials from other departments as well as hundreds of members of the armed forces as a contingency workforce to try to mitigate the effects of the strikes. The chief operating officer of Border Force, Steve Dann, has not ruled out airport closures in a worst-case scenario, and he said the travelling public should expect disruption. Just under 9,000 flights are now scheduled to land at the six affected airports – Birmingham, Cardiff, Glasgow, Gatwick, Heathrow and Manchester – during the strikes, carrying up to 1.8 million passengers, according to data from the aviation analytics firm Cirium. Officials will also strike at one seaport, Newhaven in East Sussex. The airports are confident that the contingency staff and e-gates, which will be unaffected, will process most passengers effectively during the strikes. The volume of passengers travelling through airports is still only about 85% of pre-pandemic levels. Heathrow expects departing flights will see little or no impact, with all terminals open as normal, but warned that incoming travellers should be prepared for longer waits in the immigration hall, particularly if they do not have passports that can be used at the automatic gates. Meanwhile, Royal Mail said it would do all it could to ensure delivery of last-minute Christmas cards and parcels, as tens of thousands of postal workers strike again in an increasingly bitter dispute with its staff in the Communications Workers Union. Royal Mail said the industrial action, which will have covered 18 days this year by Christmas, had now cost it £100m. A spokesperson said: “Over the next 48 hours we will be doing all we can to deliver Christmas for our customers. Thousands of employees from across the business have swapped their regular day jobs to help sort and deliver the festive mailbag. We are grateful to them and the more than 12,000 posties who returned to work on the last strike day.” A CWU spokesperson dismissed the claim and said the industrial action was strongly supported. The Royal Mail spokesperson added: “We urge the CWU to seriously consider our pay offer of up to 9%, and to work with us to bring the company back to profitability … [Its] future and all our employees’ jobs depend on Royal Mail modernising so that we can better serve customers’ changing demands.” The CWU has accused Royal Mail of refusing an offer to suspend the strikes. Its general secretary, Dave Ward, said the company was trying “to destroy the jobs of postal workers and remove their union from the workplace”. The two sets of strikes follow action earlier this week by nurses and ambulance workers. Industrial action including an overtime ban at train operating companies has continued to disrupt some rail services severely, while more rail strikes at Network Rail follow from Christmas Eve.