Before sending out a postal order in the United Kingdom, you have to cross it so the recipient doesn't get it exchanged for cash. The purpose of postal order crossing is to avoid fraud and theft. A crossed postal order is deposited directly to a bank account. By comparison, an uncrossed postal order is as good as cash in the hands of anyone who gets hold of it.
Fill in the postal order particulars, including recipient’s name and bank account details.
Draw a diagonal line on the front of the postal order. Start the line from a point almost 4 inches right of the top left corner of the postal order.
Stretch the line to a point that is roughly 2 inches right of the bottom left corner of the postal order.
Draw another diagonal line parallel to the first one, about a half-inch from the first one.