As to the efficacy of the vaccine, I'm not sure I have seen any data on it recently, but clinical trials suggested that it was 90% effective, or in or above that region, in most cases (increasing with a second dose). I would expect a similar efficacy to be seen across the larger population, but the sad truth is that we will have to wait a few weeks in order to see this effect, or indeed its absence.
It shouldn't be controversial that having no response whatsoever, or having no vaccine whatsoever, would have led to a crisis an order of magnitude worse in every sense: in terms of the total number of Covid-related deaths; in terms of those who got ill, recovered, but are suffering long-term consequences of the illness; in terms of the medical services in this country and in many others being stretched to breaking point leading to even greater shortages in care for other diseases. The irony of this post, too, is that Johnson has repeatedly tried the 10CS approach -- in March last year he refused to act for at least two weeks after being warned that a full lockdown was necessary; in September and October he refused to introduce any kind of control measures, that back then may have been needed for a couple of weeks but ended up lasting a full month in November; in December he refused to introduce lockdown because of an obsession about saving Christmas. On each occasion, the delay has cost lives. Far from being Canute, Johnson has been Aethelred, never ready to take decisive action* when it was needed, and only when he was forced into it.
*Yes, I know "Unready" in this context means "badly-advised", but in this case Johnson got the best advice possible in the circumstances but kept dithering, so I'm using the modern meaning of Unready.