No it isn’t gerrymandered. And if it is very slightly accidentally gerrymandered in some places, that works against the Conservatives - Labour MPs often have smaller constituencies.
So no that’s not relevant or part of what is being talked about here.
The reality is that 43% popular vote for a single party in a system with four major parties, 10 percentage points more than their nearest rival, is nothing but an enormous popular vote landslide. The Conservatives are popular amongst broad sections of society, incomes, ethnicities, regions. All other parties serve limited niches so are fundamentally constrained.
Why don’t they form a coalition? Well I’m not sure they really have deeply shared values to do that. Many struggle to share values internally!
You're right that there is comparatively little gerrymandering in the UK, but the political decision of how many members of parliament there should be does have a partisan bias. The Conservatives had planned to reduce the number of seats in parliament, which would have the effect of making each constituency (district) bigger and thus more rural. They had to abandon that scheme, though, after enough of their own MPs feared that their constituency would disappear from the map. There are still other controversial redistricting plans in the works though.[0]
> The reality is that 43% popular vote for a single party ... is nothing but an enormous popular vote landslide.
As I responded above, this is more attributable to vote splitting between parties that are much more similar to each other than they are to the Conservatives, and that collectively enjoy a greater share of public support, not to mention the feelings of tactical voters and non-voters who feel disenfranchised due to living in a "safe seat".
A more meaningful figure would be that the median Conservative MP was voted for by only 37% of eligible voters (in the 2019 general election), although both that number and your 43% are less than the popular vote share received by the loser of the 2020 US presidential election.
[0] https://www.theguardian.com/politics/2020/jun/02/uk-governme...
Can you explain more about this? Is the UK heavily gerrymandered?
EDIT: It's an honest question. I don't know anything about UK politics, other than that it's a parliamentary constitutional monarchy.