Individual Savings Accounts (ISAs), introduced in 1999 by then-Chancellor Gordon Brown to replace Personal Equity Plans (PEPs), have enabled thousands of savers to build substantial tax-free wealth over the past 25 years. Currently, more than 5,000 UK investors hold ISA portfolios worth at least £1 million each.
Record Growth in ISA Millionaires
The number of ISA millionaires has risen sharply from 570 in 2016 to 5,070 today. Research from investment platform InvestEngine highlights that the 25 wealthiest ISA holders average £11 million each in their accounts, demonstrating exceptional long-term growth potential.
The Proven Path: Stocks and Shares ISAs
Every ISA millionaire achieved this milestone through a Stocks and Shares ISA. No millionaires emerged from Cash ISAs, despite Britons directing more annual contributions to these lower-risk options.
Cash ISAs: Safety with Limits
Cash ISAs offer capital protection similar to standard savings accounts, with all interest tax-free. However, their returns lag significantly over time. The top 25 Cash ISA holders average £600,000, far below stock-based portfolios.
For context, someone maximizing the ISA allowance annually since 1999 would hold about £418,000 in a Cash ISA with average returns. The same contributions in a Stocks and Shares ISA would yield approximately £1.36 million.
“Those who consistently invested their full ISA allowance in Stocks and Shares since 1999 are now over three times better off than savers who did the same using Cash ISAs,” states Andrew Prosser, head of investments at InvestEngine.
Strategic Choices by Age and Risk
Pensioners often favor Cash ISAs for steady income and protection against market volatility, prioritizing the best available rates. Younger investors building long-term wealth benefit from equities’ historical superior returns.
The current £20,000 annual ISA allowance operates on a use-it-or-lose-it basis, with the deadline approaching at midnight on April 5. Regular contributions, even modest ones, compound tax-free, shielding gains from potential policy changes.

