At the same time it prevents us in the foreseeable future from deploying capabilities which have real strategic and tactical flexibility and military relevance, such as proper aircraft carriers, effective naval and airforce combat aircraft, MPA, proper AAR etc.
The defence of the UK? We seem to have forgotten how to go about doing that. Carriers have limited relevance to the defence of the UK.
Against an adversary with SSNs they'll last a few days in the open ocean. Against an adversary with SSKs and strike aircraft on the continental shelf the clock will also be ticking. They're just bigger more valuable targets. They require a lot of manpower - compromised aircraft - and a long logistic trail.
They're not about defence but politics or going after an adversary without submarines and strike aircraft.
If that's tactical flexibility - then it's a luxury to have after you sorted out defence of UK. Worse - it's a tactical flexibility that can within the next decade probably be delivered by other means using a smaller carrier designed to operate drones and backed by SSGNs.
And in the midst of this we seem to have forgotten the issue of confidence. The deterrent is ultimately one big shreiking hysterical "we will F*** you if you come near us" - that works if your adversary is convinced that you will use it. And if it comes to it as long as they have food and enough life left in the kettles they can skulk off to whereever they need to in order to deliver some instant sunshine to somebody you decide not to like on the other side of the planet. In a really nasty world that's real flexibility.