Royal Mail are the sole providers of postcode information and Dartford Borough Council do not have the ability to change or alter your postcode unless asked to do so by Royal Mail.
When a new address has been created the Council informs the Royal Mail Address Development Centre who will allocate the new postcode. They will not issue postcodes for new properties or change or alter your official address unless requested to do so by the Local Authority.
Royal Mail are also the providers of the Postal Address File (PAF) database which is used to power most online address lookups, for example, for online shopping or registering on a website. If your address is not listed, it could be that PAF does not have it as a 'live' property or that the service provider has not got the latest PAF update.
To check if your property is listed on PAF, you will need to use the Royal Mail website -
http://www.royalmail.com/find-a-postcode or you can contact Royal Mail Customer Services on 08456 045060.
Dartford Borough Council cannot update PAF themselves nor do they have any control over how PAF is distributed or often it is updated.