Operation Witchcraft is unconvincing
The plan by Karla and the mole is to use the Operation Witchcraft to make it look like Polyakov is working for the British when, in fact, the mole is providing information to Karla. The mole has a perfect cover for passing information to Karla because he can always claim that he was receiving information from Polyakov at the safe house.
My question is, how did the three stooges think that they could protect the location of the safe house from the rest of the Circus? In the BBC version, Smiley was constantly on guard against possible shadows at all times even while he was interrogating Toby. So what guarantee was there that the top three men of the Circus were not followed by someone whenever they visited the safe house?
Also, the Witchcraft arrangement can't have an indefinite life span. It must come to an end at some time. What, then, were Karla and the mole going to do?
I don't know if le Carre explains this aspect in the book. But I would have appreciated if the film explained how Percy came by Polyakov. What convinced Percy and the rest that Polyakov was genuine? Did they really believe that Polyakov was truly selling out the Soviet Union? If they did, the true talented spook in the story is not the mole, but Polyakov, because he succeeded in pulling the wool over the rest.
I can't avoid thinking that the secret to the success of the mole and Karla was not so much their ingenuity, but the Control's loss of grip over the Circus. If the Control maintained a strong grip over the Circus, the unfortunate series of events would not have happened.