I look after a number of divisional websites for a uk based membership organisation and what we want to do is provide, as well as other address functions, is a closest member lookup to a web user from the websites themselves.

A few use cases that I want to fill:

Case 1: The user puts in their post code and wants to see all the members in a 5/10/15/20/30/40 mile radius from them

Case 2: The member puts in an area (city, county, etc.) and gets a list of members in that area.

Essentially what I'm looking for is a programmable API which I can code against to do:

• post code lookup and returns addresses (after picking house number for example).
• search post code + radius (5miles, 10miles etc) and get a set of applicable post codes to then join onto the membership records in the database

Any recommendations? It can be a quarterly update install on the server, it can be a queryable web service. I'm open to suggestions.

Thanks in advance