; Date: January 1, 2020
In a recent Doctor Who a little segment had The Doctor requiring the assistance of U.N.I.T., calling up U.N.I.T.'s office, and getting a message that U.N.I.T. had been shut down due to UK Government budget shortfalls. (I looked to see which episode that was but couldn't find it.) At the time that seemed to be a throwaway political gag since The United Kingdom is currently going through an utterly crazy time.
However - in Skyfall, the season opener for Season 12 - we find ourselves in a cockamamie scheme cooked up by The Master. See: Skyfall is not Skyfail in Doctor Who Season 12 first episode
The scheme looks to involve subverting the worlds governments for some as-yet unexplained reason. To prepare for that event, The Master arranged to kill off a bunch of "spies" from spy agencies around the world.
Clearly killing the spies was about weakening the ability of world governments to respond to his plan. But why would The Master have stopped just at killing off spies.
That is, U.N.I.T. has existed for most of Doctor Who's existence, and it is tasked with countering extraterrestrial threats. U.N.I.T. has thwarted other cockamamie plans by The Master. Therefore The Master surely must have wanted to disable or eliminate U.N.I.T. if his plan meant disabling the ability of world governments to respond to his plan.
That means, we do not know how The Master managed to arrange the destruction of U.N.I.T. but it's clear from the episode that he probably did so.