UNIT HQ, City of London

By late 2023, the branch of UNIT that operated in the United Kingdom had its headquarters (TV: ) located in the City of London, near the Gherkin. (PROSE: ) It had a helipad. (TV: )

History
The previous headquarters was destroyed during the Master's Dalek Plan when Tegan Jovanka and Kate Stewart initiated the structural termination system to implode the building and entomb the Cybermen lead by a cloned Ashad. (TV: )

The UNIT HQ was among London's skyline by the time the Meep's attempted Destruction of London was thwarted by the Fourteenth Doctor, Donna Noble, and her daughter Rose. (TV: )

Behind the scenes
This UNIT HQ, going off the on-screen geography seen in, appears to be located the financial district of the City of London. However, upon analysing the position further, it makes less sense as it can be seen that and  are located to the immediate area east, the  north, the  and  to the south, and the construction site of  to the west, thus placing the skyscraper in the middle of Leadenhall Street.

Furthermore, the UNIT HQ seen in is located where the Leadenhall Building is in real life; the road Ace parachutes down towards is Leadenhall Street. The Star Beast (set in late 2023) creates a minor continuity issue by showing that the Leadenhall Building is among London's skyline, despite that tower being non-existent during The Power of the Doctor (set in 2022). The Star Beast also posits that UNIT was able to clear the site of their imploded HQ, deal with the Cyber-Warriors entombed within, and construct their new tower all in the space of a year.