Who is "them" in your scenario? The entire British public? They didn't get a say in the matter. It was a small group of politicians and business folk. And as always, they are not the ones crying now because they made bank in the deal, no doubt.
Not sure how much money they made selling their stake on the company, but if Wikipedia's valuation for Acorn and ARM are correct, can't be more than a couple of million dollars.
Those shares would be worth many billions of dollars today.
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Why do you think the brits have anything to do with anything?
If ARM ends up being bought by NVIDIA, that would actually be this Hermann Hauser's guy fault for selling ARM for pocket change. Complaining that their buyer's buyer's buyer now wants to make money with those shares by selling them to the highest bidder is sad. If ARM was so important to him, then maybe they shouldn't have sold their stake on it in the first place... Making a show about it now is like complaining that your ex that you dumped now has a new boyfriend.
... and probably lots more that I don't know about since I'm not from the UK. Blaming the misled and uneducated masses for this kind of thing just doesn't work.