The dramatic details of how the SAS completed a “brilliant” rescue of a British aid worker and three other female hostages in Afghanistan can be revealed.

Defence sources said the “surgical” operation showed the “precision, skill and courage” of British special forces after they stormed the cave where Helen Johnston, 28, was held, and killed her kidnappers.

David Cameron spoke individually to the soldiers to thank them for an “extraordinarily brave” mission. He warned that anyone who took British citizens hostage faced “a swift and brutal end”.

Miss Johnston, a committed Christian, along with Moragwa Oirere, a Kenyan colleague, and two Afghan women who worked for the same aid agency, were said to be physically well after their ordeal.