Martin Sorell's S4 Capital down after first-quarter revenue falls
** Shares of Martin Sorell's ad group S4 Capital SFOR.L fall as much as 16.7% to 35p ** Stock set to record biggest one-day pct fall since September 2025, if current losses hold ** Co posts a 5% fall in Q1 like-for-like net revenue, driven by client caution amid the Middle East conflict and reduced marketing spending by technology clients ** Co reiterates annual outlook ** Stock has risen about 84% so far this year (Reporting by Yamini Kalia in Bengaluru) ((Yamini.Kalia@thomsonreuters.com))