Robert Peston: The PM's lockdown rules would dictate delaying June 21 easing by two to four weeks

The prime minister’s road map rules would logically dictate not moving to stage four of lockdown easing on June 21 but delaying by two or four weeks.

Because the increase in the R transmission rate to more than one is driven in part by the stage two and stage three easing and not just by the greater transmissibility of the Delta variant.

As vaccine minister Nadhim Zahawi said on the Peston show last Wednesday, the more significant characteristic of the Delta variant is that one vaccine dose is not terribly effective against it, though two doses provides decent protection.

And that good protection kicks in two or three weeks after the second dose.

So with all vulnerable groups targeted to have both doses by 21 June, the government would want to add a fortnight to that date before fully unlocking.

That would also provide another fortnight of data to reassure that increased infections are not translating into significantly increased hospitalisations.

Want to hear more from Robert? Listen to Calling Peston

The case for a four week delay is that with R already above 1 because of the surge in mobility caused by stage two and three easings, it would be prudent to delay full unlocking till schools and universities have broken up in July, because that should naturally reduce the social mixing that spreads the virus.

So, for what it is worth, my view is that when the PM is in Cornwall this weekend for his summit with G7 government heads, a chunk of his brain will be choosing between a two and four week delay to full unlocking.

I simply can’t see him pressing ahead with unlocking on 21 June.