Doctor Who season 12's premiere confirmed that both UNIT and Torchwood are defunct - but just what does that mean? The world of Doctor Who is roughly analogous to our own, but there's one crucial difference; alien invasions are par for the course, and the world's governments have taken measures to protect themselves from extraterrestrial threats.
The Torchwood Institute was founded back in 1879 to protect the British Empire from alien enemies, to capture advanced technology, and of course to arrest the Doctor (who was perceived as one such alien threat). It's remained a shadowy force for centuries, with Captain Jack Harkness becoming a key member in the modern period. More recently, in the mid-20th century the United Nations formed an organization called UNIT, the United Nations Intelligence Taskforce, and various incarnations of the Doctor even served as UNIT's scientific advisers. But it looks as though both groups have now been wound down.
In the Doctor Who season 12 premiere, Jodie Whittaker's 13th Doctor is summoned by C, the head of MI6. C explains that the world's intelligence services are under attack by an unknown alien force, and confirms that both UNIT and Torchwood are defunct. Doctor Who season 11 had previously established that UNIT had been shut down, a result of austerity and the fall of multilateral ideas like the United Nations. But this comment reveals that the U.K., and probably the entire planet, no longer have any defense against alien threats at all. Presumably former UNIT and Torchwood agents like Kate Stewart have been reassigned, or else made redundant.
It's hard not to see this as a commentary on contemporary politics. After all, multilateralism is very definitely out of fashion in the real world, especially in the USA and the United Kingdom. As a result, global issues such as climate change and the refugee crisis are being poorly handled. It seems that, in Doctor Who, the defense of the entire planet has also ceased to be a priority. "Spyfall" hints that other nations have followed Britain's example, closing down agencies who are analogous to UNIT and Torchwood; after all, otherwise C wouldn't have been authorized to turn to the Doctor.
This has the effect of removing a safety net for the Doctor and her friends. They have literally become the Earth's one defense against extraterrestrial threats, and there's no longer anyone for them to call upon for back-up. "Spyfall" has made the situation even more dire, with alien assassins neutralizing the world's various intelligence agencies. The one person the Doctor turns to for help turns out to be an old enemy, reinforcing the sense that in this brave new world, the Doctor really can trust no one.