OK, I've got to the bottom of this after calling EE, who transferred me to Apple technical support, who transferred me to a second Apple support person in the iTunes (Apple Music) department.
The short answer is that it is working fine on both my Android phone and my iPad Air. The longer answer explains my confusion.
On my Android phone, after clicking the applemusic.com/ee/welcome link that I had received by text message from EE, I eventually (see earlier posts) got a screen full of music, showing that Apple Music was indeed activated. But when I go to the top-right of the screen and bring up the Account dialog, the first section is Subscription but there is nothing shown there.
On my iPad Air, if I go to the top-right and show the Account dialog and click on Manage Subscription, it shows that I am in a 7-day free preview of Apple Music Voice. In fact, this is out of date since I was in that trial months ago but not anymore.
Essentially the problem is that since the subscription was not purchased through Apple, the Apple Music user interface in both cases is not showing a subscription. But it works anyway.
