Data on transmissibility of the "English variant"?

Does anybody know where to find good solid data on the fact that the “English variant” is actually more transmissible/contagious?

Some background on my doubts (forgive the huge wall of text), in the hope that somebody can help me dispel them.

When here in the UK the government suddenly announced that a new variant was discovered and needed tougher restrictions, my personal impression was that this was a political move. In other words, the government needed to justify the U-turn on lockdown since the current measures were not strong enough and the month long English national lockdown had not slowed down the epidemic enough.

By the end of December, Imperial published a report asserting that they estimated the new variant to have an increased Rt of 0.4-0.7.

Mid January, a report has been published showing that the new variant has become dominant in some of the areas where the epidemic was advancing fast. The data covered only the period up to January the 5th.

Over and over has been repeated that some of the mutations of the new variant can be associated with an increase in transmissibility.

To this day the government officials claim that the new variant makes the lockdowns less effective.

So far, so good, here are my doubts though:

  1. The imperial report is effectively estimating the _past _ R rates of the new variant, which does not necessarily imply that the future ones will be the same.
  2. If a variant becomes dominant by mere chance, measuring the R rate after the fact will show an increased R for the dominant variant. It’s basically survivorship bias, but is quite neatly shown in this paper with a fairly simple simulation
  3. As explicitly stated in the Mid January report above, the UK monitoring system is, by mere coincidence, particularly apt at detecting the variant, which is a possible source of observer bias (we see this variant getting dominant, because we are particularly good at seeing this variant).
  4. The 30 days national lockdown in November and the current one in England are way less strict (more shops are allowed to be open) and less effective than the one in March, as per the mobility data that the government uses. I am preparing a dashboard sourcing google’s mobility data, but the gist of it is that even now way less people are working from home (there is a drop of 35% against the baseline, while in April it was 70%). Up until Mid December, furthermore, use of public transport was way higher as well.

As an added doubt, way weaker than the rest, I can use the very same super simple models for short term forecasting of the epidemic curve, and they show no particular anomaly.

Summing up, we are in a correlation/causation conundrum. The following are true:
More contagious variant ==> Higher R observed for the variant
More contagious variant ==> Variant becomes dominant
Variant becomes dominant ==> Higher R observed for the variant

We have observed higher R for the variant and we have observed it becoming dominant.
We know that the mutations involved might cause a higher contagiousness. But essentially all the observed facts can be explained without recurring to anything ad hoc, like a new more contagious variant.

Occam’s razor would push me into the idea that the new variant is not more contagious, but the precautionary principle would push me in the opposite direction (and when the first data came in, this to me was the correct principle to apply).

I am surprised, though, that after weeks, the higher transmissibility has not been confirmed with stronger data (as far as I can tell, for example, it should have been relatively easy to get in vitro results by now). And in fact I cannot find no new data at all in January.

Am I missing something?

Did you already come to some conclusions?

Data from Denmark seems pretty convincing to me, so my Bayesian posterior is “yup, it’s more contagious” at this point. But I am still surprised that given the importance of the thing there has not been more thorough research