Dear Helen, I am writing to thank you, with all my heart, for the guidance, unswerving friendship, endless laughs and crazy disco-dancing to Kool and the Gang, spanning 40 years. We first met when I, a stroppy, 16-year-old wiseass, tried to psych out you, a callow, 25-year-old teacher, on your first day as my sixth-form tutor. I was impressed that you did not flinch under my well-honed barrage of sarcastic put-downs, but instead made me laugh out loud. I was…