"For decades the BBC denied that job applicants were subject to political vetting by MI5"

BBC:

But in fact vetting began in the early days of the BBC and continued until the 1990s

...

The fear was that "evilly disposed" engineers might sabotage the network at a critical time, or that conspirators might discredit the BBC so that "the way could be made clear for a left-wing government".

...

If staff came under suspicion only after they had been employed by the BBC or applied for transfer to a job that needed vetting, an image resembling a Christmas tree was drawn on their personal file.

...

The Christmas tree was eventually dropped in 1984 because it was said to attract too much attention.

"The 'Most Dangerous Architect in America' Built a House—Then It Vanished"

Artsy:

Upon digging into the documents, it quickly became clear that Ain and his family were the target of three decades of surveillance. Documents relate that even his babysitter reported his family to the government, suspicious of the “literature” in their home and noting that they “seemed to be in some sort of group.”

...

By the time Ain began working on the MoMA house, he knew that this L.A.residential project was dead in the water, as it had been denied government loans because it was racially integrated.