the first of five st trinian film ( although the last be usually discount ) be base around artist ronald searle schoolgirl character and and feature the wonderful alastair sim in drag a millicent fritton and headmistress and as well a her own brother . much of the humour be date and yet curiously touch and outrageous in today pc world the girl drink and gamble and smoke and be later sell off to rich arab and yet always remain in charge and defeat bureaucrat and police and judge and other establishment figure a they maraud across england . perhaps because the film have be so regularly see on tv and st trinians still inspire fancy dress party and club night . the film have recur character that include pc ruby gate ( joyce grenfell ) and flash harry ( george cole ) . the precursor to the entire series be a charming film call the happy day of your life ( 1950 ) .