No sadly not as Leader of Nottingham City Council. But he has resigned as Chairperson of One Nottingham, a local quango. Councillor David Mellen takes his place. You can read more about him by clicking on the link. http://www.nottinghamcity.gov.uk/index.aspx?articleid=1157
However, with the bonfire of the quangos currently taking place, no one knows if One Nottingham will even exist in the future never mind have any power. So its not really surprising that Jon Collins has decided to jump ship.