Try rebooting your router, leaving it off for five minutes. Force close the Sonos app too. Sometimes a broadband provider might issue a WAN IP that isn’t UK registered. I would often have my devices/sites thinking I was in Germany because of this. So a reboot will ensure you get a new WAN IP address that hopefully will ensure your Sonos system can show all UK services. 
It might not be this, but worth a try.

Tried yesterday, router was off for an hour (for other reasons than just trying to get a new ip), still missing the service. 

I am having exactly the same issue. How do we resolve this issue? I’d hate to return the item because i can’t listen to BBC radio on it.

Use this link to check your location is correct based on your public IP address:

https://www.maxmind.com/en/locate-my-ip-address

Do you have iPhone? Can you listen using BBC Sounds App using your ISP WiFi?

I often use BBC Sounds App on phone and AirPlay to Sonos.

I have a UK public IP, and i do not have an iPhone.

Double check your profile:

https://support.sonos.com/en-us/article/missing-music-services-when-adding-to-sonos?language=en_US

All fine. UK address. But it wasn’t set when i installed the app. I have since reinstalled the app after clearing cache etc, but it has made no difference.

When you go to add services, do you see other UK services, eg KISS or Virgin Radio UK?

no other UK services are shown.

OK, that suggests your Sonos profile has not updated your country, as you mentioned your country was not set when you first installed Sonos App.

I would logout, uninstall, reinstall and login again, if still no UK music services, I think best to call Sonos Support.