The postal order number is located on the bottom of the front of a postal order. Sources suggest that the 20 digits grouped together is the barcode and the 10 digits grouped together is the order number.Postal orders up to £250 can be bought and redeemed at UK post offices.ostal orders are valid for 6 months. Phone 01246542254 to check if one you've purchased has been cashed. In preparation for the holidays, the last posting dates for UK Christmas 2012 delivery are: First Class-Thursday 20 December; Second Class-Tuesday 18 December; Special Delivery-Saturday 22 December.