Question about UK Employment Law. Please see below.?

I have worked in my current job for approx 9 weeks and am still on a Probationary Period - (13 weeks). I work as an Import Clerk and I am one of three staff in the Import Dept. Basically and Importer buys a Product abroad, send the documents to us and we do the Customs Entry and arrange delivery of goods. This is how it works for all customers...except one. For this customer, the EXPORTER who the Importer buys from stays in possession of the goods until they send us a RELEASE EMAIL to auhthorise us to do the delivery. We are not to deliver until the Exporter in NZ says so. I have been told by my Manager that if I was to ever deliver one of these containers without permission from the NZ Company (say I just simply forgot...this is the only one of our customers that works this way...and i am fairly new), I would be instantly sacked for GROSS MISCONDUCT and could go to Prison. Is he exaggerating and if not would I be charged with? Surely I can refuse to deal with this particular company...having said that, am I correct in thinking I have no rights until I have been employed by an employer for at least 12 months? Any ideas??