Hi,
Thanks for your suggestions. We eventually managed to sign into the App.
1. Settings>WiFi >Off,
2. Settings >Mobile Data >On,
3. Settings >My Virgin Media App>Mobile Data >On,
4. Settings >Settings>Your Name>iCloud>Private Relay (Beta) Off.
But the App will only be usable while settings 2, 3, & 4 are as above.
We had not clocked that Private Relay was on.