Facebook investors have called on the company’s chief executive Mark Zuckerberg to step down as chairman, following reports that the company hired a public relations firm to smear its critics by drawing links to George Soros.

The attack on Mr Zuckerberg is set to complicate the daunting challenge facing Sir Nick Clegg, Facebook's new global head of policy and communications, who joined last month and has been asked to conduct a review of Facebook's use of lobbying firms.

Jonas Kron, a senior vice president at Trillium Asset Management, a US investor which owns an £8.5m stake in Facebook, last night called on Mr Zuckerberg to step down as board chairman in the wake of the report.

“Facebook is behaving like it's a special snowflake,” he said. “It's not. It is a company and companies need to have a separation of chair and CEO.”

Both Mr Zuckerberg and Sir Nick have been under pressure following reports Facebook hired Definers, a Republican public relations firm, to help repair its battered reputation following intense criticism of the social media platform's handling of a scandal over Russian interference in the 2016 US elections and the Cambridge Analytica scandal.