Mr Johnson has previously said the Royals “are beyond reproach” on the campaign trail and is likely to bat away any chance of weighing in on the rift that has split Buckingham Palace.
It comes as the UK recorded fewer than 100 new daily Covid-19 deaths for the first time since October 19 with 82.
Boris Johnson said he hoped Monday’s tentative softening of restrictions marked a “big step” on his “road map to freedom” – a plan which could see all Covid measures lifted by June 21.
As well as pupils returning to classrooms for the first time in at least two months, the rules around meeting with a person from another household outdoors will be loosened to permit recreation and not just exercise.
While the “stay at home” message will remain in place, it means people can leave home to meet one other person for a coffee or picnic.
The Prime Minister, in comments made to the Daily Telegraph, said that even though it was “only a small relaxation of the rules”, this week’s changes would bring “joy and relief” to families after months of “tough restrictions”.
It came as a leading children’s doctor warned that schools can only open safely if everything else “stays locked down” for at least three weeks.
Professor Russell Viner, president of the Royal College of Paediatrics and Child Health, told Times Radio: “Sage has concluded that reopening schools adds probably about 0.2 or thereabouts to the R number.
“We know that reopening schools will increase transmission, but we should be able to keep the R below one – and, as you’ll recall, that’s the key thing to stop the runaway increase of infections.
“It’s very plausible, in fact I think very likely, that we will keep the R below one with schools open with these mitigations in place.
“And I think the key thing is that children themselves, and parents, don’t think ‘The schools are open, we can relax, we can mix outside of school’ – in a sense, come out of lockdown around the school opening.
“The modelling – and I think the Government has been clear on this – is about we can reopen schools safely if everything else stays locked down over the next three weeks.”