Treble One, the only defence against a mass raid on UK, bolt from the blue, would be response in kind. The only high alert response is Trident.
Game, set, match or score draw.
The V-Force could mount an effective retaliatory response in 4-5 hours (other than QRA), I think the air defence force was a couple of hours faster. Apart from QRA neither force could meet the bolt from the blue.
Today many things have changed. Fewer fighters; fewer bases(targets); more people live off base with many over an hour away.
Is there a plan? Don't know. I do know we hung into the Fortress Britain plans just in case. In a remarkably short time they became out of date. Squadrons equipped, changed bases, units moved, and there was no high level interest in maintaining what were essentially history documents.