Television cameras were allowed inside the offices of MI5 for the first time as the security servivce hosted a visit from a group of Blue Peter competition winners.
The young trio were selected as part of a scheme on the children's programme called Project Petra, which saw them go into MI5's headquarters at Thames House on their first "mission".
Finley, 10, from Surrey, Jamie, 13, from Glasgow and Reuben, 13, from North Yorkshire were given a tour of the building.
They were also shown a range of spy gadgets and met the director general of MI5, Andrew Parker.
Jamie said: "Before going into MI5 I felt really nervous but excited at the same time because I knew no kids or TV cameras had ever been in MI5 before. It felt really cool because we were making history that day."
Eight candidates were chosen out of over 5,000 applicants and attended a CBBC Spy School weekend in Manchester in March.
The final three were then selected from this group by children's author Anthony Horowitz, TV presenter and journalist Sonali Shah and Professor Christopher Andrew, the official historian of MI5.
Blue Peter editor Ewan Vinnicombe said: "The judges were so impressed by the abilities of all eight candidates at CBBC Spy School but what really stood out with the final three was their communication skills, their ability to work as a team, which is key to being an intelligence officer, and also how they were able to solve problems quickly and calmly.
"I hope the audience at home will enjoy watching too and that Project Petra will help them understand more about the world in which we live."
The special edition of Blue Peter will be shown on April 16 at 5pm on CBBC.
