I need Integration of HTML Form with Postcode Lookup Service API

You'll see that there are two addresses on the form, thus it should be possible to use the postcode checker on both addresses. The form is the output from a lead management system, therefore please work around the code that's already on the page and make sure it would not conflict with the postcode check code.

jQuery is available in the page.

The form must work like this (for either set of address fields):

1) User types in a postcode as well as clicks a button next to the field.
2) A select box appears to show all the addresses under that postcode.
3) User makes a selection to fill all the address fields in and hide the select box.
4) (The user can repeat the process if necessary).

Desired Skills are HTML, Javascript, jQuery, HTML5, API