Clue: Marks & Spenser talk about introducing new stores initially (6)
Answer: STAINS
Explanation: Definition: Marks

**S**(penser) **T**(alk) **A**(bout) **I**(ntroducing) **N**(ew) **S**(tores) [*initially*]
 

 
*The Spenser in the clue should of course be spelled Spencer.