Personally though I need a couple of questions answered, what would have happened if McVie had not left Mayall? Would McVie have only come in when the band was famous, and would Brunning have been so gracious if the band were famous by the time McVie wanted in? Would the rest of the band even want McVie say 12 months later when they had become a close knit group?
Apparently the only two ways that McVie would have left Mayall were:
Mayall turning away from pure blues (which of course was the real reason)
OR
Fleetwood Mac being stable and profitable enough for McVie to leave the security of Mayall...
So the reason that Bob Brunning is still not in Fleetwood Mac is because John Mayall likes to experiment!
