The prologue of Power of the Daleks
According to this, a UNIT clean-up crew arrive at the Snowcap Base to check things out. We're told that they make a cursory search for the three people who saved the day and then vanished, then shrug and move on, because the Cyber-technology is much more interesting.
This is pretty weird piece of callousness on UNIT's part. What's even weirder is that there's a much better explanation available — if UNIT, and especially a squad that includes Benton and Sarah Jane, were told that the three missing persons were a mysterious figure who called himself the Doctor and his two companions (and there's no reason why they wouldn't be), they'd probably make a pretty good assumption as to what happened to them. Instead the book implies that UNIT didn't make that connection, and didn't much care.
