NHS Covid app and Huawei, or why I *can* blame Trump if I get Covid-19

I got a second-hand Huawei phone about two months ago.
Unfortunately the NHSxxxSerco Test and Trace app refused to set itself up, reporting:
Unfortunately, you can't run this app

This could be due to:

A restriction in your settings (for example, if this is a company phone).

Another app on your phone is using the same technology and stopping this app from working.

Turns out that the problem is that the US block on Huawei means that Google cannot make the Apple/Google Exposure Notifications System available on this phone.

Pity the message doesn't say that.

Grr.