The Times reports M&S were breached through a contractor and that human error is to blame. (Both M&S and Co-op use TCS for their IT Service Desk).
The threat actor went undetected for 52 hours. (I suspect detection was when their ESXi cluster got encrypted).
M&S have told the Times they had no “direct” communication with DragonForce, which is code for they’re using a third party to negotiate - standard practice.
https://www.thetimes.com/uk/technology-uk/article/m-and-s-boss-cyber-attack-7d9hvk6ds