Entirely possible. It's sometimes useful to remember that even in today's "open" world (The fall of the Soviet Union made it a lot less like active warfare even in the spooks still roam free) there will still be huge amounts of material known only to those on the inside.

In the 70s there was an unannounced (to the PM) "terrorism drill" on Heathrow Airport, that some have alleged was a practice run for a potential coup against Wilson (I don't think that holds much weight, but it's not impossible)