The current silicon chip shortage is showing just how dependent we are on chips, and while Arm doesn't have their own fabs, they are an important part of that ecosystem. There's a good chance that the current drought may play a role in US decisions on dealing with the China/Taiwan issue, if China shows aggression there is now a clear national security incentive for the US (and other countries, for that matter) to intervene and protect Taiwan, just like they did with oil for the last 40 years.

given that, it's entirely reasonable that the UK doesn't want ARM gutted and the IP shipped out of the country.