There is no long term lease - Some time in the 90s Bill Dore surrendered it to the council and it was extinguished (or he failed to comply with it, and the council revoked it - take your pick).
Speedway occupied the site under a series of short (7 year?) leases, the last of which expired in 2008.
Option on the new site expired and speedway ceased to be part of council's plans for redeveloping the area. The land was there, the money wasn't.