Question about last episode whodunnit bit (SPOILER!) - Hope someone is still reading this site! ha

Due to sound issues in the tape to YT transfer version I watched, I was not able to discern a lot of dialogue in the final episode.

So...of the two code names Bernie surmised were for traitors high within the UK....one was we know Fiona and the other indeed was.....Brent?

That was Bernie's original thought of course, but he also seemed to wonder if the careful crafting of Brent as the second traitor also was done to mask another more important traitor in the UK's midst.

The convo between Bernie and Brent at the flat in Berlin after Brent does a midnight flit across the Channel seemed not that conclusive to me as to Brent being Number 2 Traitor,but maybe it was the sound quality that made me miss the conclusive nature of their talk.

Did K7 plant the papers in Brent's house, for instance, simply as icing on the cake to be sure Brent the traitor was easily convicted? Or was he indeed totally set up?

Has anyone read the books to know if Brent was indeed the second traitor? Or was he being set up to cover another big fish?

Thanks!