Every spy thriller has a few plot holes and you need to just ignore them and just enjoy the action. But this series has so may preposterous situations and developments that after a while it just becomes utterly worthless as entertainment.
Just a few ridiculous examples - we are to believe that a Russian master agent is so traumatized at the loss of 5 operatives that she abandons her career and spends the next 15 years trying to track down who was responsible for their deaths.
A British agent is credibly accused of being a double agent and what does MI6 do? It promotes him to deputy chief.
The current head of MI6 is poisoned and the culprit is identified but from that point on she not only eludes the combined forces of MI5, MI6 and the Metropolitan police but she freely roams around all of London without a care.
The CIA decides to send a team of agents to investigate the poisoning of said MI6 chief and it just so happens that the lead agent is a best buddy with the wife of the newly promoted MI6 deputy chief.
That newly promoted MI6 chief roams all over London without a bodyguard and on the few occasions when he does have bodyguards he easily slips right past them and no one thinks it is the least bit strange.
The Russian super agent, after evading all those combined forces out looking for her, attempts to retrieve a cache of weapons and cash and doesn't notice that 2 agents are walking up to capture her until they are literally standing directly above her.
A meeting of the intelligence committee of Parliament is held in a building which just anyone can walk into - which the widow of the former MI6 deputy chief does, clutching a super secret trove of intelligence data.
The British Foreign Secretary decides to plug in the drive containing all of that material (which is embarrassing and highly compromising to all sorts of bigwigs) and display it on the screens for the entire audience to see.
And there are dozens more such examples.
I can only imagine that the writer of this decided to see just how utterly preposterous a script he could come up with and still get fans to swallow it.