Apple has updated earlier iPhones to work with contact tracing apps - though apps that use the Apple-Google system will need to be updated to be compatible with the OS update. 

The update to iOS 12.5 means that iPhone 5 and iPhone 6 series phones will be able to use contract tracing apps - though as we said the apps themselves need to be reworked. The BBC suggests that new versions of the apps for the NHS in England and Wales, Scotland and Northern Ireland should emerge in January but that's unconfirmed. 

At launch, the apps were largely blamed for the lack of compatibility with older phones, but it wasn't actually the apps that were at fault, because the decision to not support the older devices was down to the underlying tech developed by Apple and Google in a unique partnership

Apple and Google call their contact tracing system COVID-19 Exposure Notifications, essentially because iPhone and Android device owners can receive notifications about whether they've been exposed to people diagnosed with COVID-19.

Apple rarely updates iOS for older devices, but it does release occasional security updates and indeed with iOS 12.5 the release notes say "this release also provides security updates and is recommended for all users".