6pm press conference, delayed to reduce competing with football, widely expected to announce four week delay. Example
https://www.independent.co.uk/news/uk/home-news/what-time-boris-johnson-announcement-b1865244.html
R rate is 120-140% so it's spreading again and now mostly the delta variant, which hasn't hit hospitals too hard yet but I've heard reports that there are worries about how delta will affect hospitals, both in bed occupancy and in health workers having to isolate, which sounds like
gov.uk aren't confident that both the "Infection rates do not risk a surge in hospitalisations which would put unsustainable pressure on the NHS" and the "assessment of the risks is not fundamentally changed by new variants of the virus" tests are passed just now.
I'm slightly surprised that they seem to be shaping up for a four week delay, rather than a "we'll look again in two weeks but prepare for a further delay".