Initial reports on the first day of strike action by Border Force officials suggested minimal impact on airport operations during the morning peak arrivals period.
The walkouts will affect border checks from today (Friday) to Boxing Day and then between December 28 and 31.
They are taking place at Heathrow, Gatwick, Manchester, Birmingham, Cardiff and Glasgow airports, in addition to the port of Newhaven.
Earlier on Friday, Mark Serwotka, general secretary of the Public and Commercial Services (PCS) union, warned the strikes could last for six months unless pay demands were met.
Aviation analytics firm Cirium said the festive walkouts could affect a total of 8,910 flight arrivals, equating to more than 1.7 million seats.
Although the action will impact those arriving in the country, there are fears that any delays could have knock-on effects on aircraft rotation and departures as traffic builds.
Military personnel and civil servants were drafted in to cover passport checks and reports from the two biggest airports, and Sky News said Heathrow, Gatwick and Glasgow airports had reported minimal disruption.
The BBC also said operations continued to run smoothly in the early afternoon, while Birmingham airport told The Independent the maximum wait time during the morning peak had been 18 minutes.
Elsewhere, ground handlers at Heathrow confirmed they had called off strike plans over the New Year period following a pay deal with Menzies.
However, members of the Prospect union working for Elizabeth Line operator Rail for London Infrastructure (RfLI) confirmed they planned to strike for 24 hours from 6.30am on Thursday, January 12.