HM Gov. would surely ensure they keep it in reserve for response use to anything big going off in London?
That's what many people thought about Halton after it's use for Op OLYMPIC and potential for other requirements in London. It has/had the capability to generate accommodation for thousands (if you sent the recruits home), an unrivalled ability to train people for ceremonial (or other duties) and you could reach London in under an hour (at suitably unsociable hours).
Even that, together with the apprentice history and tradition at Halton, wasn't enough to save it from the housing plan.
Is Northolt all that different?