Even the BBC seem to be saying that this is fake:

Hmmmmm

If you were in charge of the country's secrets would you tell a minister who fires everyone who disagrees with you? Come on, MI5 are not about opinions, and prejudice - their job is to get the facts. Ya canna let the incredulous loose with facts. Geeze. Ya spoon-feed them. With facts ya want let loose. Agents' lives are at stake.