The system will rank the threat level from coronavirus on a scale of one to five and be adjusted according to data. Boris Johnson is due to give a televised address updating the nation on the progress of lockdown measures. The PM is expected to unveil a new slogan, telling the public to "stay alert, control the virus, save lives". He is not expected to provide exact dates for when the restrictions - first announced on 23 March - might change. The new system will apply to England only but the government is working with the devolved administrations as they develop their own. It is understood the system - with alerts ranging from green (level one) to red (level five) - will be similar to the one used to keep the public informed about the terror threat level. Mr Johnson is expected to say England is currently at stage four but moving towards stage three. The warning tool - to be administered by a new "joint biosecurity centre" - will also reflect the virus threat in different parts of the country, meaning the threat level in one city could differ quite widely from another.