Fascinating article basically confirming what you might suspect - MI5/6 have press officers who conduct deniable off-the-record briefings of pet journalists at the major papers who, in return for the privilege, behave nicely.
http://www.newstatesman.com/politics...ence-briefings
I can guess the BBC ones and I know the Telegraph's Con Coughlin has long been wedged up MI6, but who are the others?