"If we introduce this next stage too early, the measures will not protect us at the time of greatest risk but could have a huge social impact. "We need to time this properly, continue to do the right thing at the right time, so we get the maximum effect for delaying the virus. We will clearly announce when we ask the public to move to this next stage. "Our decisions are based on careful modelling. We will only introduce measures that are supported by clinical and scientific evidence."