The decision to go ahead with the mega mail-out was confirmed on Saturday evening (28 March).
The letter from prime minister Boris Johnson reiterates the existing advice to “stay home and save lives”, but also states that people unable to work from home can travel to and from their place of work.
He also says: “We will not hesitate to go further if this is what the scientific and medical advice tells us we must do.”
The leaflet condenses existing advice and guidance into easy-to-read information in one place, with links to specific guidance in England, Scotland, Wales and Northern Ireland.
The mammoth print job is being managed by APS Group, which is believed to be working with a number of printers to complete the task as quickly as possible.
Sources said Communisis and Go Inspire Group were understood to be among the printers involved.
BPIF chief executive Charles Jarrold commented: “In this very challenging and difficult time, at least the government continues to put their faith in print. We have been highlighting to them the key and essential role that print plays in so many ways, and they clearly see it as the most effective way to communicate out this vitally important message.
“In the message the prime minister again reiterates that the government will do whatever it takes to help us all make ends meet; we welcome what's been done so far, but we are also communicating clearly where these steps do not meet sector needs, with so many businesses under such acute pressure.”
The first letters should start to land on doormats from the middle of this week, according to a Number 10 spokesperson.
APS had not commented at the time of writing.
There is growing concern about the number of online and email scams that have sprung up, with fraudsters aiming to take advantage of people during the virus crisis. After the government issued an official text message last week, fake messages began appearing shortly afterwards.