There were just three ISA millionaires in 2012 on the Hargreaves Lansdown’s site in 2012.

Today, there are 168 investors with £1m or more in their ISAs, the group revealed.

Sarah Coles, personal finance analyst at Hargreaves Lansdown, said investors have benefited from increasing ISA allowances in recent years.

“However, building a million pound ISA portfolio isn’t just about putting your full allowance in and banking on a rising market. Successful investors have built a coherent strategy, taken a sensible amount of risk, been committed during the difficult times, and adopted a long-term view,” she said.

Coles added: “If you look at the most commonly held funds and shares in millionaire portfolios, they’re not jam-packed with super-high risk assets. They have balanced mainstream portfolios, positioned to take advantage of growth opportunities, without going overboard.”

The most popular shares in million pound portfolios

In alphabetical order, here are the most popular shares held by Hargreaves Lansdown’s ISA millionaires:

• Aviva plc
• BP plc
• GlaxoSmithKline plc
• Legal & General Group plc
• Lloyds Banking Group
• National Grid
• Rio Tinto plc
• Royal Dutch Shell plc B Shares
• Unilever plc
• Vodafone Group plc

The most popular funds in million pound portfolios

Again, in alphabetical order, here are the most popular funds held by Hargreaves Lansdown’s ISA millionaires:

• Artemis Income
• Fidelity Special Situations
• Fundsmith Equity
• Invesco Perpetual High Income
• LF Woodford Equity Income
• Lindsell Train Global Equity
• Marlborough Multi Cap Income
• Marlborough Special Situations
• Marlborough UK Micro-Cap Growth
• Stewart Investors Asia Pacific Leaders

Top steps to help you build a million pound ISA portfolio

Coles lists these top 10 steps to help your ISA portfolio reach the £1m mark:

1) Start now

£1 million may feel a long way off, but the only way to move it closer is by making a start on your investments. You don’t need to have enormous sums to invest on day one, small regular savings will soon start to build up and you can commit to revisiting how much you invest whenever you can afford to do so.

2) Use as much of your allowances as possible

In the last few years, the allowances have increased dramatically. There is, however, no knowing how long that trend will continue. It means it’s worth using as much of your allowances as you can afford each year, to take advantage while you can.

3) Reinvest dividends

This has a profound effect on overall returns, because you are compounding the growth on your assets. If you’re investing in companies that aim to grow the dividend, you will effectively magnify that growth.

4) Take enough risk

If you’re putting money aside for ten years or more, your money has a far better chance of growth in the stockmarkets than in a cash ISA, although your capital will be at risk. You can also increase the potential upside by considering more adventurous assets for your portfolio.

5) Exploit the globe

One way to expose your portfolio to more potential growth is by investing some of it in emerging markets. These are generally riskier investments than those in more developed countries, but in return they can tap into economies with the potential for faster growth.

6) Don’t go overboard

If you take big positions in risky stocks or other assets, you need to be prepared for the potential losses as well as the possibility of gains. Adventurous assets should only be used in a way that suits your overall attitude to risk.

7) Use an expert

There are ISA millionaires who are individual stockpickers, but most people prefer to use the expertise of a fund manager. While tracker funds are an excellent way to get started with the stockmarket, many of these more experienced investors, with much larger portfolios, have selected a recommended manager who runs a relatively concentrated portfolio. That way they have the potential to amplify growth, without necessarily having to become an expert themselves.

8) Don’t chop and change too much

Investing is a long-term process, and while it’s important to keep an eye on performance to ensure it’s meeting expectations, it’s also vital to take the long view. Switching investments in an effort to time the markets will bring higher transaction costs and may mean you miss out on the long-term growth story of a fund or share.

9) Stick out the tough times

Building a large and successful portfolio is about time in the markets rather than timing the market, so when things are more difficult, the key is to buy rather than sell.

10) Don’t forget the rest of the family

In addition to your own ISA, you should also make sure your spouse is using theirs, and that you have put money into Junior ISAs for any children. A family of four can shelter £48,256 in the current tax year by using their allowances.