Welcome to the community and thanks for posting on the forums. I'm sorry to hear you're having difficulties getting network service on your handset. Sometimes it can happen when the phone comes back to the UK after being away.
A good first step is to give the phone two or three hard reboots in a row just in case it’s still searching for the networks you were connected up to whilst abroad. If that doesn't resolve the situation, then it's also worth doing a manual network search on your handset and manually selecting the Virgin network.
Hope this helps but let me know if you're still having difficulties.