M&C Saatchi shares dived after four bosses at the advertising giant, including its co-founder, quit the firm in the wake of an accounting crisis.
Shares slipped 5.1% to 97.3p in early trading on Wednesday after Lord Maurice Saatchi, who launched the business with his brother Charles in 1995, resigned.
His resignation on Tuesday evening was announced alongside the departures of fellow directors Lord Dobbs, Sir Michael Peat and Lorna Tilbian.
Lords Dobbs, a conservative politician, is best known for writing the House Of Cards novel.
Jeremy Sinclair, chairman of the company, said: “We are determined to restore the operational performance and profitability of the business and are already implementing all of the recommendations set out in the PwC report we announced last week.
“We had started a process to reconstruct our board with new independent directors.
“This new board will have a mandate to conduct a full review of all aspects of our governance.”
Their exits come just a week after the firm warned over profits after being hit by higher costs and a weak performance in the final quarter.
This was the second profit warning for the UK firm in the past three months and came after it launched an internal review into the accounts of its UK subsidiaries in August.
M&C Saatchi said it would restructure its UK business in a bid to improve performance.
The company also said it would face an £11.6 million one-off hit as a result of the accounting review.
Separately, it had said that PwC identified its 2018 half-year profits were overstated by around £6 million.
The Saatchi brothers originally made a name for themselves with a number of major campaign posters for Margaret Thatcher, who Lord Saatchi later described as his “favourite client”.