The union said staff employed by the government in passport booths would take action at Heathrow and Gatwick airports as well as Birmingham Airport, Cardiff Airport, Glasgow Airport, Manchester Airport and the Port of Newhaven.

The union's General Secretary Mark Serwotka said around 2,000-3,000 staff would be involved in the walk outs on Dec. 23, 24, 25, 26, 28, 29, 30 and 31.

Asked why the union had picked the Christmas period to take industrial action, the union chief said: "those people will lose pay when they go on strike, they do it as a last resort and the job of the union is to ensure that the action that we call is noticed."

(Reporting by Farouq Suleiman, writing by Sarah Young; Editing by Kate Holton)