As members of the PCS union who work for UK Border Force prepare to go on strike, The Independent has identified the days and locations when pressure will be highest.
Staff who normally check the passports of arriving passengers will walk out on 23-26 and 28-31 December inclusive in a row about pay, pensions and job security.
Heathrow, by far the busiest of the airports, will feel the effects most strongly on the first day of the strike.
According to calculations from the flight data specialist Cirium, 583 flights with 126,700 seats are scheduled to arrive at Heathrow on 23 December. While the actual number of passengers will be lower – because not every seat will be filled – the figure will concern officials who are seeking to put mitigation in place.
As at all airports, Christmas Day will be the quietest of the strike days, with just 83,400 passengers on 352 flights. But Heathrow returns to full stretch from 28-30 December, each with around 125,000 passengers on 575 flights.
At both Gatwick and Glasgow, arrival numbers are highest on the two Fridays in the strike calendar, 23 and 30 December. Gatwick expects over 60,000 arrivals on 325 flights, while Glasgow anticipates more than 10,000 passengers touching down aboard 85 planes.
At Manchester airport, where bosses are already warning that some flights will be cancelled, the peak is expected on Boxing Day: 37,000 passengers on 191 flights.
But every day apart from Christmas Eve and Christmas Day will be extremely busy, with an average of 35,000 passengers on 180 flights.
At Birmingham, the key dates are 23 and 31 December, with over 16,000 arrivals, but 27, 29 and 30 December are also expected to see more than 15,000 passengers touching down.
Cardiff’s peak day will be Tuesday 27 December with 1,300 passengers on nine flights; 30 and 31 December are also looking relatively busy.