The biggest individual donor to the Brexit campaign has lost more than £400m in the share price meltdown that has hit stock markets since the result of the EU referendum was revealed.

Peter Hargreaves, the billionaire founder of financial advice firm Hargreaves Lansdown who gave £3.2m to the Leave.EU campaign, has seen the value of his shareholding in the FTSE-100 listed company fall by 24%.

Although now retired and no longer an executive of the company, he owns 30% of its shares. But since Thursday, when they were priced at £13.89, the shares have slumped to just £10.56, knocking more than £400m off his £2bn holding.

“The shares have suffered a fallout just as everything else has. Hargreaves Lansdown has fallen quite a lot,” he said,

But he added that he had no regrets about backing the campaign to leave the EU: “I didn’t do this for personal gain. I thought it would first and foremost be good for Britain.”

Hargreaves welcomed the fall in sterling, which has hit lows against the dollar not seen since 1985. “It will be the biggest stimulus for British business that I’ve seen since 1992. For FTSE 100 companies, many of whom make their earnings abroad, when those earnings are translated into sterling, it’s going to make them very profitable.

“After we left the exchange rate mechanism in 1992, we rose from the ashes like a phoenix, and by 1997 had a trade surplus and a balanced budget. Why should it be any different now? Suddenly Britain’s much more competitive, even if they put tariffs up against us.”

But Hargreaves condemned the politicians on both sides of the Brexit campaign, and the political chaos since the result of Thursday’s vote. “I’m afraid the actual politicians in the leave camp most of them were in it for political expediency. Was Boris Johnson doing this for any other reason but to become prime minister? He shouldn’t be PM, he only did it for expediency. I’m rather hoping that the government will be sensible enough to find people [for the negotiations] who have some experience of business.”

Hargreaves is in favour of Britain retaining access to the EU’s single market, and thinks a deal will be found to protect the City’s banks and financial services. But he said there was no going back on the result of the referendum. “I think there will be an enormous amount of anger from the leave camp if anything like that is tried,” he added.