Part of these changes to tax law was the change in the balance of power between social classes.
Just prior to WW1 you had to be over 25 and male to vote, and this was actually a reform from previous generations where voters also had to own real estate too.
Such things kept electoral power well out of the hands of the lower social orders.
The closest thing we had to representation for working class people was the Liberal party, and it was a series of critical votes and elections prior to WW1 that demolished the power of the House of Lords on its veto over parliamentary made law.
This effectively emasculated the power of the aristocrats - the land owning classes. Further changes such as being salaried as a Member of Parliament also made it possible for representatives of working classes to put themselves up for election.
This was pretty much the culmination of a class struggle where those who produced British wealth had virtually no say in how it was distributed, or in the laws that they were governed by. Throughout the 19thC various repressive measures and hard won liberalisations of law came about partly through philanthropy, perhaps through fear that denial of representation could lead to revolution - in any case workers organised themselves into trades unions, and the need for an increasingly educated skilled population all came together to loosen the ties of power.
The fear of revolution was justified, after all we only need to look at Europe, and Russia in particular to see what can happen once workers start to organise
After WW1 we had the final change to democracy to allow women to vote - and again this then made it possible for political parties to represent workers directly, instead of through a social proxy such as the Liberals.
You have to remember that living conditions for workers were absolutely dreadful, prior to WW1 a full 30% of children did not make it to adulthood, and average lifespans for those in the lower classes were decades shorter than those in the gentrified classes.
WW1 revealed the extent that Britain had truly slipped away in industrial power, it also revealed the disproportionate privilege of the landed classes. Social change such as improvements to housing, education, sewerage and clean water were glaringly necessary - the problem was how it was to be paid for.
That’s when the relatively recent idea of income tax (used to fund WW1 itself) was extended, and in turn along came death duties - when the Labour party looked at where it could leverage money for all this it was also seeking social changes, the idea of huge wealthy estates that were in effect just dead money the view was taken that this should be redistributed and invested.
Personally I see the imposition of death duties and subsequent collapse of estates as being very similar to what Henry VIII did to the church, it was a transfer of wealth from wealthy landowners to government, and in both there was an overt intention to change the social structure of Britain.