Write a tweet mentioning "Spooks" or including hashtags like #BBCSpooks and one or more of the regular main characters from the series will follow you and may well reply to your tweets.
From the boss, Harry, to agents like Ros, Lucas and Dimitri and Ruth who rarely gets away from the Grid your favourite Spook is now just a tweet away.
Given the content of some of the tweets I doubt the BBC are running the campaign.
I suspect this also rules out Kudos who produce the series.
Whoever's doing this it's fun and creating a bit of online buzz around the start of the new series on Monday.