The Prime Minister said outdoor markets and car showrooms would be able to open from June 1 if they are safe to do so.
All other non-essential retailers – such as those selling clothes and books – will be allowed to open from June 15, provided the guidelines are met along with the Government’s five tests for easing the lockdown.
Mr Johnson told the daily Downing Street press conference that the risk of transmission is lower in outdoor areas, where social distancing can be easier to enforce.
Earlier this month, garden centres were permitted to reopen in England, Wales and Northern Ireland as part of the easing of coronavirus lockdown restrictions.
Join our new coronavirus Facebook group for the latest confirmed news and advice as soon as we get it The Prime Minister said: “We will set out our formal assessment of the five tests that we set for adjusting the lockdown later this week as part of the three-weekly review we are legally required to undertake by Thursday.
“But because of the progress we are making I can, with confidence, put the British people on notice of the changes we intend to introduce as we move to step two.”
He said new guidance was being published for the retail sector “detailing the measures they should take to meet the necessary social distancing and hygiene standards”.
“Shops now have the time to implement this guidance before they reopen,” he said.
“This will ensure there can be no doubt about what steps they should take.”
Mr Johnson said the authorities would “have the powers we need to enforce compliance where that is required”.
“I want people to be confident that they can shop safely provided they follow the social distancing rules for all premises,” he added.
He urged people to go to the shops to help the economy bounce back.
The Prime Minister said: “I’m certainly not going to discourage them from spending at all.
“I think that it’s early days but we are very much hoping there will be a bounce back over the next few months.”
Helen Dickinson, chief executive of the British Retail Consortium, said: “We welcome the announcement of the Government’s road map for reopening a broader range of shops next month, which provides much needed clarity on the route ahead.
“Safety is the fundamental concern for all retailers and they have been working hard to implement the necessary measures to operate safely over the past weeks.
“Now that we know which shops can open and when, retailers can begin communicating their plans with their workforces and customers. The industry stands ready to play its part in getting the economy moving again.”