Littlepom, the genie's out of the bottle now, so I agree with the others who say don't lie. These things have a habit of catching up with you particularly in the OASC interview - they will get you if they think you're not being straight. Remember your personal integrity!
Beags, I agree with your policy of not wanting drug abusers in your UAS, but as someone who these days works a great deal with what I suspect was Littlepom's agegroup at the time of the 'incident', the attitude towards drugs is not the minority, fairly hidden thing it once was and I do think that for Littlepom to try it and then decide it's not for him shows at least a reasonable strength of character given the peer group mentality I observe. I speak as someone who went through university mildly disappointed never to have been offered drugs in order that I could refuse! On the other hand, having seen the effect that regularly smoking cannabis for even a short time does to the reactions and situational awareness of young people, I wouldn't have let them within a mile of a 'dog (or Teutor - must keep up with the times!).