This is the council's side of the argument. https://www.lewisham.gov.uk/inmyarea/regeneration/deptford/north-deptford/Pages/New-Bermondsey-questions-and-answers.aspx
And Millwall's www.millwallfc.co.uk/documents/replacement-leaflet98-1341310.pdf
Both a short read.
Millwall are not moving to Kent, not now and probably not ever. The talk of a move is just to get people on their side.
Millwall want to develop the area around the ground themselves, this is all about who makes the profit, the council or the football club.