Score-settling by the ousted (and then returning) CEO Malcolm Walker. After Iceland merged with Booker in 2000, Walker was pushed out and a new management team led by Bill Grimsey took over. Sales declined, head office staff ballooned and they hired a lot of McKinsey types. Walker's point is that they'd overcomplicated what was basically quite a simple business.
I worked for a public sector organisation around then that had the same chairman (not CEO) as Iceland, sorry, “the Big Food Group”. He was genuinely one of the most obnoxious, bullying people I’ve ever encountered - known internally as the Poison Dwarf. So none of this greatly surprises me.
Interestingly the "dark ages" subpage is not linked from the parent page: https://about.iceland.co.uk/our-story/
Grimsey was boss of Iceland, but also, Grimsey is in Iceland:
https://en.wikipedia.org/wiki/Gr%C3%ADmsey