Fidelity Personal Investing calculated that savers who use the new £15,000 annual allowance could have £1m sheltered from the taxman in their 25th year of investing instead of 29 years with the current allowance of £11,520.

George Osborne announced the increased ISA limit in his 2014 Budget. He also gave savers more freedom to be able to combine cash and stocks and shares savings.

How to become a NISA millionaire

While there are few ‘quick fixes’ to becoming a NISA millionaire, Maike Currie of Fidelity Personal Investing says, the top tip is to maximise your allowance and properly diversify your portfolio.

Currie said: “Investing in cash is your least risky option. However it is often said that no one ever became a millionaire by leaving their money in a cash account, and with interest rates at historic lows this is truer than ever.”

She points out the importance of holding some cash as a rainy day, but adds that the returns on stocks and shares speak for themselves.

Fidelity calculated that if a saver had invested £15,000 into the FTSE 100 All Share Index over a 10 year period they would now hold £35,218.50. By comparison a £15,000 investment into the average UK savings account over the same period would yield just £16,582.65, a difference of £18,635.85.

Currie explained: “Over a long time horizon the ups and downs of the stock market can be smoothed out. These figures show that investing in equities would have earned you thousands more, compared to saving through cash over the past 10 years. For most savers, that will be too big a discrepancy to ignore.”