Earlier when asked about why the govt didn't act earlier the PM said “I think we were told about the new variant and the way it was taking off on 18th December and we went into T4 across the vast bulk of the country pretty much in the next 24 hours.”

This isn't entirely correct.

The new variant was identified in early December after genome data was paired with a curiosity that the rates of infection in Kent were not falling despite national restrictions and then T3.

So there was indicative sense that the variant may be playing its part as early as that and perhaps sport greater transmissibility.

On December 14th Matt Hancock informed the Commons, saying the new variant was in at least 60 local authorities already. https://www.bbc.co.uk/news/health-55308211

He told MPs in that over that week, there had been sharp, exponential rises in coronavirus infections across London, Kent, parts of Essex and Hertfordshire.

He said they couldn't be sure whether that was due to the new variant but that caution was required.

As a result, London and several other places in the South East were moved to T3.

On 18th December NERVTAG reported that they believed the new variant was indeed more transmissible.

On the 19th, the govt acted. This is the action I assume the PM referred to today.

The government introduced a new tier, tier 4 and extended it to much of the south east.

But as you can see, it certainly didn't include "the vast bulk" of the country

Indeed- areas just adjacent to T4, in East Anglia, were still in T2

Then on December 23rd, the govt acted again- extending T4 to all of the south east of England. But swathes of the country were still in T2 and much more in T3.

We know during this time the new variant was seeded elsewhere- but some of those areas still had lighter restrictions.

It wasn't until December 30th that the government put most of the country into T3/4. And only this week that we had a full lockdown.

So it's not true as the PM said "we went into T4 across the vast bulk of the country pretty much in the next 24 hours" on December 19th. That would take until 30th and arguably not until this year.

Two other things to remember 1) given govt was aware the new variant might have greater transmissibility before NERVTAG reported, some argue it should have shown greater caution before this date in any event 2) some public health experts say that even without...

...the new variant, the tiers as was, wouldn't have been enough (especially with planned Xmas relaxation) to prevent significant pressure on the NHS in January- (though prob not the appalling situation we now have)

Given those winter pressures and how bad things now are and will become, the workings of the tiers and their timing are of no less public importance than the timing of the March lockdown. Indeed, I suspect they'll come to be scrutinised just as heavily in the years to come.

PS massive credit as ever to the peerless @ElectionMapsUK for the gfx

Further proof from the ONS that the limited T4 SE measures did not work in containing the new variant, either in the SE or preventing its further spread elsewhere. https://twitter.com/lewis_goodall/status/1347610702509469701?s=20

We'll never know what the counterfactual would have been if the PM had, as he said yesterday, put the "vast bulk of the country" into T4 on the 19th, when the govt found out about the greater transmissibility- or gone into national lockdown.