They Don't Know What They Are Doing!
Although they Chinese own it, all of the staff operating it will be British and probably wouldn't obey orders to turn the plant off in times of tensions with China to make a political point.
That assumes that there no remote control to turn it on or off.
Nest and Hive work autonomously and have remote control.
Building remote control in at the design stage would be a trivial task, so don't think Huawei wouldn't do it.
Also think: if these things have GPS and individual serial numbers and a small amount of intelligence then they will know when their kit is close to the American embassy/GCHQ/name your vulnerable site and message back to China. Is the traffic at the edge encrypted or in clear? This kit will be handling massive amounts of data, so we can't tell what is "standard" data traffic and what is control data. The control data or tapped traffic won't be visible because of dilution. And it doesn't _have_ to go back to China, it could just as easily go to a location under Chinese control with high security, so it may be in a business shed near you.
Who is doing the thinking about this?
This is a one way ticket and once you've lost control, you'll never get it back.
They say Huawei are about two years ahead of everybody else. I say we could easily wait two years!