### Clue: Writer becoming expert on soldiers in retreat (6)
### Answer: ARCHER 
 ### Explanation: Writer becoming expert on soldiers in retreat (6)
ARCH ("expert") on <=R.E. (Royal Engineers, so "soldiers", in retreat) 
Probably refers to Jeffrey Archer *aka* Baron Archer of Weston-Super-Mare, but could also be Geoffrey Archer, who writes spy and adventure stories.