Leicester Hounds/Leicester Stadium (1931 & 1937): Folded mid-season in 1931, with further issues in 1937.
Liverpool Merseysiders/Chads (1937 & 1953): Withdrew mid-season in 1937; record expunged. Also closed in 1953.
Ashfield Giants (1952): Closed during the 1952 season.
Cradley Heath Heathens (1953): Disbanded mid-season in 1953 following the withdrawal of the promoter.
Hackney Hawks (1983): Folded mid-season in 1983.
Long Eaton Invaders (1997): Closed during the 1997 season.
Trelawny Pitbulls (2003): Folded mid-season in 2003.
Oxford Cheetahs (2007): Folded mid-season in 2007.
Mildenhall Fen Tigers (2010): Experienced a mid-season closure in 2010.
From Wikipedia, any takers in the Den?