However, markets will keep going higher before they collapse, he argued.
“We are still in the early stages of a bubble, as several conditions for a bubble are not yet met. There is still plenty of money on the sidelines, borrowing is low and – although stock market enthusiasm among individual investors and the media is increasing – we are nowhere near the frenzy we saw in the 1990s,” he said.
Professional investors are still optimistic about the stock market. ARC Research, an analyst which tracks the investment decisions of wealth managers with over £15bn in assets between them, found that investors were overwhelmingly positive about the stock market’s prospects for the next 12 months.
Its latest sentiment survey revealed 78pc of investors were “positive” about stocks while 86pc were “negative” about bonds in the face of rising inflation.
Daniel Hurdley, of ARC Research, said: “Managers view stocks as the main source of investment returns, showing positive sentiment towards all geographical regions. In terms of sectors, the most healthcare and financials are currently the most popular.
“The negativity on bonds means that managers are diversifying into other assets. Hard commodities, including gold, are very popular, and investors are also showing increased interest in private equity.”
Mr van den Heiligenberg said he was also bullish about the prospects for stocks.