In London, a house/flat is not a Ferrari, as pps have said, unless you sell it and move somewhere a lot cheaper.
Most London property-owners live Ford Focus lives in Ford Focus houses.
When they die, it's the bank of Dead Mum and Dad - or Granny - that enables their offspring to continue living an ordinary life in the capital or suburbs. Bear in mind, that the cost of living in London is higher than elsewhere - not just housing, everything from the commute to childcare to softplay, and the 'London allowance' doesn't go anywhere near making up the shortfall.
Ime, unlike the hypothesis in the Spectator article, inheritance is passed down the generations to get on the housing ladder, not to become buy to let landlords. But perhaps I move in less affluent circles. And the dcs/dgcs are often buying Ford Ka not Ford Focus properties with the proceeds.
When the current threshold means that the children of nurses and teachers, perhaps nurses and teachers themselves, are losing 40% of the surplus, then it's too low. London is increasingly becoming a capital of extremes. Those who would have had social housing in the past are being shipped to the midlands, and a creeping exodus of public service workers will not improve the social mix.