Sounds more like 'massive over-reaction aimed at playing on people's worst fears' garbage spouted by a newspaper on the journalistic race down to the bottom rather than 'massive security breach'.
Let's think about this rationally.
A plane full of security screened passengers arrive from an airport that has screening as good as if not better than the UK who then come into contact with a load of passengers who have already been security screened at Manchester.
It's a c*ck-up yes; embarrassing for the management yes; inconvenient for the passengers of course but 'massive security breach' ? ..do us all a favour and save the hyperbole for actual meaningful security breaches.
The trouble with society now is that we have lost the ability to think straight; the slightest mistake or malfunction is seen as a pre-cursor to the end of mankind as we know it. Journalists demand heads roll, politicians jump on the self-righteous bandwagon and solicitors lick their lips at the prospect that they might convince people to sue for 'hurt feelings' or some other made up form of alleged harm.
Lessons need to be learned, resources need to made available if that is seen as a contributory factor; better training too but panicking and over-reacting serves no purpose.
What ever happened to 'Keep Calm and Carry On' ?