It is in the lease, the OP said there is a specific clause in the lease saying that the dog could stay on occasion. I thought that was what the OP wanted, to have the dog there occasionally.
The landlord has backtracked because the neighbour has complained, but if it is in writing they can’t.
The missing piece is that no-one has asked the EC’s permission. So go ahead and ask, you have the landlord’s ok. In our building the landlord always does it because they are the owner, but perhaps it might be easier here if the tenant does.