I got one free with the turkey and happy to send to anyone who wants it, as we won't use it. It allows you free unlimited family entry until March 31st BUT you have to visit before January 31st to exchange the voucher for the pass.
Exact wording below:
"Day entry is normally £15 per family, this free family pass entitles you to free multiple entry to the Nature Trail until March 31st 2012. To receive your free pass, please visit Jimmy's Farm Shop before 31st January 2012 with this voucher."
Jimmy's Farm is in Wherstead, Suffolk, IP9 2AR.
PM me if it is any good to you and I'll pop it in the post.