First, let's put numbers in perspective. That "70%" figure sounds scary. But, it's 70% of a small number, namely, the R-nought number. So, using the example above, an R0 of 1.1 going to 1.5 is an absolute value increase of .4, which is an increase of 36%. If it went from 1.1 to 1.77, that would be a 70% increase. An R0 of 1.77 isn't good, but it isn't apocalyptic.
Second, while this *could be* more contagious, there's no evidence for it, except, for its current prevalence among the strains that exist. That *may imply* greater contagiousness, but not necessarily. As we always say when doing science: correlation is not causation.
Could there be other causes? Oh, yes. How about the geometric curve we're all so familiar with? As we plot the daily number of cases and see the trend line get larger, it suddenly spikes upward. That has happened with all the other mutations of COVID... so why is this spike any different? It's happening everywhere with the older mutations.
I laughed at one of the quoted articles which pointed to this geometric growth of COVID in the U.K. despite lockdowns. Um.... we have geometric growth just about everywhere despite precautions being made. Why? Because people won't stop socializing and going to indoor restaurants and bars and gyms and they think being outside magically protects them from someone next to them without a mask on.
If there is a new strain of COVID that has a R0 closer to 2.0 than 1.0, then all the hygiene precautions we've been doing should still work... if people took them seriously.