Given ARM is mostly an IP bsaed company that wouldn't really work. For reference just look at what happened with ARM's china susidiary with which this basically happened.
ARM China is a sales office. Not the same thing at all.
If a design is made in a British office of a British company, 'by hook or by crook' the state can gain access to it. That's the hard, perhaps slightly uncomfortable truth.
Of course it would only ever come to this if softbank refused to sell and there was some national security angle.
If ARM want to close their office here, then the state can hire all their engineers and offer immunity/void on any NDA they've signed with ARM, if anything that's actually the most desirable outcome.
Again we're talking about things that simply aren't going to happen, and if they do there are much much bigger problems.
