The NHS are currently texting and sending letters to everyone classed as at risk. If you're at high risk, you will be contacted by the NHS by Sunday 29 March 2020.
They have almost all received a text message by now. (A few are being reached by other means.) I know a couple of people that have received them, they’re pretty serious.
A couple of my family members received letters 2 days ago, saying they are to stay at home for 12 weeks. That's in Scotland though, so things might differ elsewhere in the UK.