Want to be a millionaire? Easy. Invest in an Isa

With tax-free savings accounts having been around since 1987, when personal equity plans were first launched, if you'd used your allowance every year and invested in the right fund, you'd be sitting on more than a million now.

You would have stashed away £203,760 – not including the current 2013-14 tax year – but if you'd put it all into the Fidelity Special Situations fund, your nest egg would have grown to £1,542,000. That would have been a profit of £1,338,240.

However, finding a winning investment is not always easy. If you'd decided to back the Scottish Widows Japan Growth fund, you'd have made a profit of just £15,240. That's a lower return than if you'd simply left your cash in a savings account.

"Hindsight is a wonderful thing and if you are in the right funds the rewards can be huge," pointed out Brian Dennehy of Fundexpert.co.uk. "But you should review your investments regularly. And if you have an adviser then you should be adding value by monitoring your portfolio."

Guy Foster, head of portfolio strategy at Brewin Dolphin, said: "Saving in a tax- efficient wrapper remains one of the most compelling ways of realising your long-term financial ambitions.

"The importance of compounding, and the benefits of tax-efficient saving, can deliver life-changing wealth to those who seize the opportunity."

Isa millionaires are those who take some investment risk, but Brewin Dolphin reckons that even savers who invest the full Isa allowance conservatively each year could reach the £1m mark in less than 30 years. Starting now, you would invest £508,773 by 2042 but – based on 5 per cent growth – would see your pot climb to £1,030,953.