### Clue: Swapping of partners in group involves drugs and is severe (9)
### Answer: SWINGEING 
 ### Explanation: Definition: is severe
  SWINGING(euphemism for wife-swapping,partner swapping – "in a group" seems superfluous, since such activity must involve 2 or more pairs, or am I missing something?) **containing**(involves) E(abbrev. for the drug ­$$E$$cstasy – I guess the plural "drugs" and not the singular is for the surface)
Defn:  British dialect for punishing,severe derived from Old/Middle English word for shake,smite,swing,blow