Bunkers are great for a small range of legacy jobs that need hardened accommodation and an ability to ride out a blast for a short period of time. For all other purposes they present an enormous pain in the backside in terms of facility management, upgrading and keeping going.
I suspect crossed wires here - BOULMER will almost certainly stay open, but perhaps the question is whether to build a new building or not. Having been inside it, I'm not sure what military advantage having it in a bunker offers in the current threat environment. Yes I know someone will go "BUT THE RUSSIANS", to which my view would be 'if the Russians are launching strikes on the UK mainland, then we all have a very short time to live".