Poor inheritance tax planning is expected to cost British taxpayers £1.3bn this year, research suggests.
A study by adviser search site Unbiased.co.uk, based on HMRC data, found vast sums are being paid unnecessarily each year because the deceased made inadequate provisions.
According to Unbiased research, it is Britain's second biggest 'tax wastage' area, and it warns the figure could increase as the IHT threshold will remain frozen for four years at £325,000, rather than rising in line with inflation.
The organisation's annual Tax Action Report also shows IHT is among the taxes Britons most want to abolish.
Karen Barrett, chief executive of Unbiased.co.uk, has urged people to consult IFAs to ensure their estates are not hit by large IHT bills.
She said: "Our report reveals that vast sums are being paid unnecessarily in IHT every year because the deceased had not made adequate provision.
"Such situations can only bring additional unwelcome stress for the deceased's family at an already difficult time, as the tax must be paid before the estate can be released and any inheritances can be passed on."
The report also shows the number one area of tax wastage is through tax credits, with over £8.5bn being lost through people failing to claim child benefit, child tax credits, working tax credits and pension credits.
Overall, it says £13.5bn will be wasted through unnecessary tax payments this year.
The figures include tax paid in error and tax which could be avoided through better management and planning.
An ambitious objective
'Something completely new'
'Illusion of control'
Reasons to be cheerful
Total investment reaches £9m