Systematic plan (6)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">systematic plan</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for scheme that I've seen before include "Secret plan, plot" , "proposal" , "Project or strategy" , "Lay plans" , "'Plot, plan (6)'" .)
(Other definitions for regimen that I've seen before include "Prescribed course of diet, exercise, etc" , "Method of working" , "Course of diet, therapy" , "Recommended course" , "Prescribed system of diet and exercise - mere gin (anag)" .)