Exactly!Harry Sullivan was a serving member of her majesty's armed forces and UNIT so he'd do what he was ordered to do...and then he'd tip the Doctor the wink about what he'd created.
Always assuming Z67 ever really existed, since it wasn't in either box and mysteriously vanished after Harry invented it...
Ooh, I like this idea. Harry is ordered to invent a gas that kills Zygons, Harry pretends to do it, and then calls the Doctor to spirit it away, thus convincing UNIT it's not worth their while to try again, because the Doctor will always turn up and take it.