While this thread has had some very detailed or technical replies, the basic fact that Britain couldn't rely on ANY aircraft borne deterrent can't be changed.
If we were talking of North Korea then the airfields would be secure places, and would be protected by an IADS. We are talking about the UK, with carriers that would require most of their air compliment to protect themselves from a major adversary and airfields that are very easy to disable.
It seems to always come as a surprise to some that the RAF could be stopped in its tracks very quickly. I've heard lots of tales of tactics using low, medium and high altitude. Heard about DAS and evasive manoeuvres but none of these worried me. I still knew the UK was a free democracy, had only a few air bases and nowhere near enough RAF regiment to protect them from organised attack.
The RAF regiment/RAF FP don't even have enough manpower to protect airfields from rifle/grenade attack, let alone anything a bit more powerful of with a slightly longer range.
The new F35 may have super duper stealth and an advanced DAS suit, but sadly that won't help an aircraft that needs to fly from a known I'm moveable base, and use a known immovable runway.
Even something that could realistically disperse like the harriers could (with non heavy loads/fuel weights) are easy to find and track in today's western society with nothing more complex than an iPhone.
Let's not kid ourselves that in an all out conflict against an organised opponent that any RAF airfield would be operational for very long. The saddest part is that by only causing very limited damage the effects would be disproportionate as the RAF has been being stripped of its damage repair capabilities in successive defence budgets.
Many of you will have seen for yourselves that SF can quite easily get themselves inside an RAF station. Some posters here have come face to face with SF on top of or within buildings on the station during exercises. When the SF are using live rounds and have indirect fire weapons it's easy to see just how vulnerable an RAF station really is.
An airborne deterrent in a Western society with free movement just isn't a credible option IMHO. It's not even a question of numbers or cost, it's simply the fact it wouldn't work. The fact we don't have an air delivered weapon, enough aircraft or a training system seem to pale in comparison.