well, ours is on land the club leases from the council..when we asked, we were told it was up to the association..ours is now 30x10..one of the other lads has a 20x10..a couple of others want one and we're thinking of a communal 30x10 for next year so's our plant sale stuff can go in it..so, it's going to be a polytunnel allotment soon ;D
tell them they will have to pay for it to be demolished, ask someone how much they would charge to take it down for you..that may make them think again..good luck, hope you get to keep it :)