S4 Capital has reported that its revenue doubled in 2021, as boss Sir Martin Sorrell apologised for the “unacceptable and embarrassing” delay in posting full-year results.Shares in the advertising agency rose almost 20% on Thursday after the company announced it would be publishing the results more than a month after it said auditors had failed to sign them off.The delay had been announced just an hour before the results were initially due, wiping almost a third off the agency’s market value.Sir Martin said on Friday that he will be making significant changes to the company’s governance and tightening financial controls...