Jeremy Corbyn wants to lower the inheritance tax threshold to £650,000
Labour wants to get rid of Tory proposals to raise the inheritance tax threshold to £1m by 2021 by imposing a backdoor policy.
The party wants to reduce it from £850,000 to £650,000 so more than one million more families would have to pay thousands more in tax on their family home when their parents die.
The plan is not in the Labour manifesto but is in a separate costings document.
Currently, inheritance tax of 40 per cent is charged on estates worth £850,000 and above.
Under Labour those inheriting £850,000 would have to pay an £80,000 'death tax' bill.
Research into the 2016 Land Registry by the Conservatives has revealed Labour shifting the threshold would mean 1.2m extra households would be hit, bringing the total number forced to pay inheritance tax to 2 million.
Under the Tories' proposals inheritance tax would hit 725,000 families.
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Theresa May's party said Labour's move would be far more damaging to pensioners than the Tory's social care plans.
They also claimed Labour wants to reduce the threshold further to £425,000, although the Labour party strongly denies this.
Housing Minister Gavin Barwell, said: "Millions of families who have worked hard and saved all their lives will see their homes dragged into Jeremy Corbyn's punishing tax."
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Mr Corbyn's costings document also reveals Labour would raise £3.7billion by reversing tax allowances implemented by the Tories.
It says it would be "reversing tax giveaways on capital gains tax, inheritance tax, bank levy and scrapping the married persons' tax allowance".
Theresa May has said the Tories will raise the threshold to £1m
The Conservatives' research found about six per cent of homes in England and Wales have a value of more than £650,000, while two per cent of homes are valued at over £1m.
With inflation, 7.7 per cent of homes by 2021 will be worth more than £650,000 and 2.9 per cent more than £1m.
Mr Corbyn did not place the policy in Labour's manifesto
Estates worth more than £650,000 will attract a large inheritance payment
If Labour then lowers the threshold to £425,000, as the Tories claim, 15.3 per cent – or 3.9m – of all homes in England and Wales would be hit.
With house price inflation this would increase to 19.4 per cent of all homes by 2022, or 4.9m homes.
Mr Barwell, added: "Jeremy Corbyn's manifesto contains a £58billion black hole and Labour will attempt to fill it using damaging taxes on family homes.
"Corbyn and John McDonnell have made clear they want even more properties to become liable for inheritance tax if they win power.
"Under their chaotic plans, one in five homes across the country would be swept up in Labour's family homes tax."