Go to postcode.royalmail.com and enter your house's address in the search form. Click "Find postcode."
Call 0906 302 1222 from the United Kingdom. This information line is available Monday through Friday from 8 a.m. to 5 p.m. and there is a per minute fee for the call.
Call 08457 111 222 from the United Kingdom. You can access this information line Monday through Friday from 5 p.m. to 7 p.m., and on Saturdays from 9 a.m. to 2 p.m. You will be charged at local telephone rates.