Lawyers at private client law firm Mills & Reeve unsurprisingly said that middle class voters will benefit if the Conservatives’ proposal ever becomes law.

Under current UK legislation, IHT of 40 per cent is currently levied on a deceased person’s estate over a nil-rate band of £312,000. The nil-rate band can be carried over between married couples, giving the surviving spouse a tax-free allowance of £624,000. However, some commentators have argued that the change was largely cosmetic because couples have been able to mitigate the impact of the tax by tax planning anyway.

The Conservatives are arguing for a £1 million nil-rate band with the ability to transfer an unused allowance to a surviving spouse.

"Surveys have repeatedly shown that IHT is one of the most hated taxes, because it is seen as a double tax charge. Individuals will have paid a lot of tax on their hard earned money as they have gone through life and resent having to pay a second charge to tax, the IHT, on death on the monies they have been able to save up,” said Matthew Hansell, head of private client at Mills & Reeve.

UK inheritance tax has been attacked because the nil-rate band has not, so critics argue, risen in line with asset prices, which meant that a growing share of the population have been drawn into the tax net, spawning a large tax-planning industry to help individuals to avoid the tax where possible.

Inheritance tax is not just an issue in the UK. Last year, French President Nicolas Sarkozy announced increases to inheritance tax thresholds under France’s traditionally elaborate IHT regime.