By Ali Lyon Sir Martin Sorrell’s S4 Capital’s post-pandemic struggles have carried through into its latest results, which revealed a sharp decline in revenue and ballooning debt. The London-listed media holding group, which ad guru Sorrell founded after a sudden exit from WPP in 2018, saw its net revenue reduce by 15.6 per cent from £445.5m to £375.1m in the six months to June 30. The group’s net debt ballooned from £109.4m in the first half of 2023 to £182.8m, some of which, the firm said, was down to the £2.5m share buy-back programme launched in January; its first ever. Billings at the ad g…