Military outfits are almost entirely monday-friday 9-5 operations, it would take a stuka attack from something very fast moving, heading directly for a military base or major population centre to sound any alarm bells in the mind of the poor guy on duty at O-silly-hundred-hours observing for credible threats.
So your saying that, if a plane took off from the UK in the night then halfway out over the sea stopped communicating and transponder stopped working on SSR, then turned back toward the UK and over flew the UK for 1 hour still with no communications, that there would not be military response ?
i am afraid i cannot see that at all, and i find it really hard to believe that is the case here