Thousands of investors who have saved diligently into Peps and Isas to take advantage of the tax perks might be better off just giving the money away — or spending it.

A new study calculates that the chancellor stands to pocket a £15 billion inheritance-tax (IHT) windfall from Pep and Isa savers when they die — nearly three times the amount of other taxes that investors have saved during their lifetime.

The average IHT bill for someone who has taken full advantage of Pep and Isa allowances since 1987 could be £116,000, according to Bates Investment Services, an adviser. But they would have saved only £42,000 in income and capital-gains tax (CGT).

Putting money into the tax- efficient schemes later in life could therefore be pointless if you want to pass it to your children, because any tax saved will be more than clawed back in death duties.

Advisers say thousands of savers, many of whom may not realise Peps and Isas are subject to death duty, should consider ways to reduce their IHT bill, such as making gifts. Paul Ilott of Bates said: “Peps and Isas are tax- efficient during your life but on death the tax shelter is removed. The amount of tax saved during your lifetime can be dwarfed by the size of the IHT bill.”

Investors were first allowed to put money into Peps in 1987. Isas replaced them in 1999, but existing Peps were allowed to continue. You could put up to £9,000 a year into Peps (although the allowance was lower in the early years), compared with £7,000 into Isas — a total of £144,200 over the past 20 years.

Since 1987 more than 19m accounts have been opened to take advantage of the tax perks. These have been watered down over the years, but capital gains are still free of tax and there are income-tax benefits if you are a higher-rate taxpayer.

When you die, however, your entire portfolio is added to your estate and you pay 40 per cent on anything over the nil-rate band, which is £285,000 this tax year.

Millions of people live in properties worth more than this, so for them all other assets, including Peps and Isas, are subject to the full 40 per cent tax.

The problem is most pressing for Britain’s growing band of Pep and Isa millionaires — those who have saved the maximum every year and have enjoyed strong returns. For example, Lord Lee of Trafford, a former tourism minister and Conservative MP, has a portfolio worth more than £1m.

Since 1987 he has invested the maximum every year.

Double-digit returns from his investments in UK smaller companies have pushed his portfolio over the £1m mark. But his heirs now face an IHT bill on these investments of about £400,000. He said: “The tax advantages of Peps and Isas have been just too valuable to squander, but there is the IHT issue. I think there is a strong case for raising the threshold over which the tax is paid.”