** British consultancy Next 15's shares NFGN.L tumble over 16% to 241p, set for largest pct drop since Sept 2024
** Co forecasts FY26 profit "materially below" expectations, revenue to be in line
** Analysts estimate FY26 revenue of 491.7 mln pounds, profit of 51.9 pence/shr, according to company-compiled consensus
** Expects lower conversion of opportunities within Mach49 business after potential serious misconduct disclosure
** Co appoints Sam Knights as CEO after Tim Dyson retirement
** YTD, stock down 38.48%
(Reporting by Unnamalai L in Bengaluru)
((Unnamalai.L@thomsonreuters.com;))