Britons will pay almost £2 billion more in inheritance tax over the next five years than previously thought, official estimates have revealed.
The Office of Budget Responsibility (OBR) believes the Treasury will take in £1.8 billion more than was forecast last November.
The change in numbers was buried in the body's twice-yearly analysis of the economy released this week alongside the Budget.
We will take the family home out of inheritance tax. That home that you have worked and saved for belongs to you and your family - you should be able to pass it onto your children
David Cameron's election pledge
Rising house prices and a booming stock market were named as the causes of the increased tax haul, withe the economy growing quicker than expected.
Critics jumped on the revelation to renew calls for the “most hated tax” to be scrapped given the Tories enjoy a majority in the House of Commons.
Inheritance tax is levied on property and financial gifts that are passed on when someone dies, with 40 per cent being the standard rate.
George Osborne and David Cameron put a promise to lower inheritance tax at the heart of the Conservatives’ 2015 election pitch to Middle England.
The pair promised to ensure that homes and other assets worth up to £1 million could be given entirely tax-free to younger generations.
Mr Cameron said at the time: “We will take the family home out of inheritance tax. That home that you have worked and saved for belongs to you and your family - you should be able to pass it onto your children and with the Conservatives, the tax man will not get his hands on it.”
Despite implementing the changes, revenue generated for the Treasury from inheritance tax is still set to soar across the coming years.
It will rise from an estimated £4.7 billion in 2016/17 to £6.2 billion in 2021/22 – an increase of around a third.
Furthermore, when those forecasts are compared to ones made just last November they are £1.8 billion higher across the period.
The OBR explains in the document: “Receipts have been revised up over the forecast period due to slightly higher equity and house prices.”
The stock market and house prices have risen faster than expected over the last six months as the UK economy defied pessimism in the wake of Brexit vote.
Paul Johnson, director of the Institute For Fiscal Studies (IFS) think tank, said more people were likely being dragged into paying the tax due to a growing economy.
“Clearly the stock market has risen. To the extent that there are any shares being inherited, that is going to have an effect," he said.
"Inflation is a bit higher and the inheritance rate threshold is fixed so that would help.
“Obviously anyone who has assets overseas they are worth more in pounds terms, I don’t know if that [is having an impact].
"But I assume housing must be driving a lot of it because that is a very high fraction of what is inherited.”
Mr Johnson said inheritance tax had “always” been a bugbear for some who believe it is unfair to pay tax on assets bought with money already taxed once.
“It is one of those taxes where people have very different fundamental ethical views,” Mr Johnson said.
“There are clearly some who think that the appropriate thing to do is to allow stuff to be passed along the generations because it had been bought out of taxed income in the first place and you don’t want to tax it again.
“That is probably the majority views I suspect. There are others who take very much the opposite view.”
Dia Chakravarty, political director at the TaxPayers' Alliance, said: “Inheritance tax is a terrible tax which hits grieving families at the worst possible time and punishes the very basic human instinct of wanting to leave something behind for one's loved ones. It is the most hated tax for a good reason and needs to be scrapped immediately.”