Willingly or not, if any potential buyer isn't breaching the terms of the lease then I think there's very little the council could do about it without ending up in court again. In essence they can't
"unreasonably" prevent a transfer (assignment) of the lease.
Of course, I guess there isn't even a transfer if ACL is purchased whole, so even less chance of the council being involved.
Below are some answers to frequently asked questions regarding tenants’ requests for alterations and assignment of their lease.
www.penningtonslaw.com
Dellah Gilbert reviews case law relating to the often contentious topic of landlords granting consent to a prospective tenant when an existing tenant wishes to move on.
www.lexology.com