It's such a miserable shame that these church people can't be more helpful and understanding.
Note that you don't have to sign any new agreement, but it would always be possible for the church to give you 12 months notice to quit if you didn't. Of course that isn't what they've done, they've just tried to forfeit the tenancy and they can't do that.
I'm very pleased you've got the NSALG to represent you. You're in the right, but defending your rights is tricky and stressful and we don't need that as allotmenteers. I mean, fair do's, there's a mess to be cleared up right enough, but the church should be talking to all the tenants about how to do it between you, and not picking on people and making up the law as they go.
Very best of luck, I'm pleased the paper got involved, it's a good piece.