Boris Johnson is writing to 30 million households with a warning that "things will get worse before they get better" as the country battles COVID-19.
His plea for people to "follow the rules" will land on the doorsteps of 30 million households across all four UK nations from next week.
He is continuing to lead the government while self-isolating in the flat above Number 11 Downing Street.
New figures released on Saturday showed another 259 people have died in the UK after testing positive for COVID-19 – with at least 13 of them having no underlying health problems.
A total of 1,028 people have died in the UK after contracting the virus.
In his letter, Mr Johnson says the right preparations are being made and the more closely people follow the restrictions, "the fewer lives will be lost and the sooner life can return to normal".
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Residents will also get a leaflet outlining the government's advice – looking at symptoms, hand washing, rules on leaving the house, self-isolating with symptoms and shielding vulnerable people.
The prime minister writes: "We know things will get worse before they get better.
"But we are making the right preparations, and the more we all follow the rules, the fewer lives will be lost and the sooner life can return to normal."