Balbir Bagria may well be the UK's most successful Isa investor.

He his wife, Jasvir, have been living off their investment income since 1999. He has outperformed top professional fund managers, despite spending just a few hours a week on his portfolio.

If you had given him £1,000 in 1993, he would have turned it into £430,000 by the end of 2017. That’s a whopping 42,900pc return over 24 years.

This has made the couple Isa millionaires, and enables them to draw a tax-free six-figure income each year.

He oversees the portfolio with help from his wife, using do-it-yourself Isa accounts. His money is invested in 10 to 15 stocks at a time.

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He aims to find companies with a recent record of earnings growth, or that are not properly valued by the market.

Over the past year, key holdings have included mining firms, which he viewed as undervalued, and small technology companies, where he found promising returns. To minimise the risk, he employs “stop losses” that sell holdings automatically if they fall below a certain point. He makes a small loss on about half of his stocks, but the stop losses mean he sells out quickly when positions sour.

“I expect a stock to make money. If it starts losing value I conclude that I’ve got my analysis wrong,” he said.

However, at the moment Mr Bagria holds 60pc of his portfolio in cash. He said: “I’m not confident the stock market has much further to go up.

“I don’t know if this is the top, but it’s not far off. There has been a long bull run, and while Trump has been good for markets so far, sooner or later a disaster will happen.”

Mr Bagria was already about 40pc in cash before last month’s market sell-off. That rose to 60pc when falling global share prices meant he automatically sold out of some shares.

He has made similar moves in the past. He moved entirely to cash before the tech bubble burst at the turn of the millennium, and was largely uninvested when the global financial crisis hit – although he still sustained losses after putting some money back into the market too soon.

He added that he has less conviction now than in 1999, “when I was 100pc sure it was a bubble,” but said that “markets can’t go up forever”.

Read more about Mr Bagria's strategy here.