Modest estates are not taxed at all.
Yes they are, if that modest estate happens to be in Fulham or Tooting or Streatham, or Wimbledon etc.
You keep on insisting that if a person can buy a two bedroom semi and afford a loft conversion and an extension that by default they are stinking rich. There are no millionaires in my close as far as I am aware, but the vast majority of these 3 bed houses are worth a lot of money because of where they are, and over the 500k threshold. Yes, if you are married and have exactly the right circumstances then you can increase that to a million.
My house started life as a 3 bed detached house. The previous owners added an extension above the garage making it 4 bed. We converted the useless garage giving an extra reception room. My neighbours have a 2 bed end of terrace semi. They are doing a loft conversion and ground floor extension. This is one reason why the next generation find it so hard to get onto the property ladder. Many people buy a house they can just about afford, then instead of moving, make it bigger.
If you moved my street to Wolverhampton IHT wouldn't be an issue for anyone.
As it is, IHT only applies to a narrow band of people. If you are wealthy enough you just avoid it because you can afford an accountant who will find myriad loopholes to ensure that no IHT gets paid on your estate. Do you think the Barclays, Lord Rothermere, RIshi Sunak, JRM etc will be concerned about IHT? Of course not. SO if you are only taxing those that have more money due to property or a bit more cash than most but not enough to dodge it, what's the point of it?