Those nice folks at Streetmap (http://www.streetmap.co.uk )  have a very handy webpage that lets you obtain the Longitude/Latitude of a UK Postcode at -

http://www.streetmap.co.uk/gridconvert.html

This is so nice for geo-encoding UK postcodes, i.e plotting customers on a map etc..   Given the flexibility of the service,   I decided to make it line-of-business friendly and wrap the postcode to long/lat lookup into a web-service.

The return string is of the form -

<?xml version="1.0" encoding="utf-8" ?>

<string xmlns="http://tempuri.org/">51.625128:-0.150448:Provided By www.streetmap.co.uk:http://www.streetmap.co.uk/streetmap.dll?grid2map?X=528126&Y=193432&arrow=Y&adkey="~"</string>

So we return a decimal longitude, latitude and a credit back to streetmap and a link to the streetmap, map.

Here's the source,   the string handling is a little brutal but it works great.

using System;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Net;
using System.IO;

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class Service : System.Web.Services.WebService
{
public Service () {

//Uncomment the following line if using designed components
//InitializeComponent();
}

[WebMethod]
public string GeoEncode(string UK_Postcode) {

if (UK_Postcode == "") return "No Input"
string lookuppostcode = UK_Postcode.Replace("-", "");
lookuppostcode = lookuppostcode.Replace(" ", "");
string request = @"http://www.streetmap.co.uk/streetmap.dll?GridConvert?type=Postcode&name=" + lookuppostcode;
string result = "ERROR"

HttpWebRequest myReq =
(HttpWebRequest)WebRequest.Create(request);

// Sends the HttpWebRequest and waits for the response.
HttpWebResponse myHttpWebResponse = (HttpWebResponse) myReq.GetResponse();
try
{
Stream response = myHttpWebResponse.GetResponseStream();
StreamReader readStream = new StreamReader(response, System.Text.Encoding.GetEncoding("utf-8"));
string htmlresponse = readStream.ReadToEnd();
string whattofind = "Lat</strong> (WGS84) </td> <td width=\"50%\" align=\"center\" valign=\"middle\">"
int indexoflonglatbit = htmlresponse.IndexOf(whattofind);
if (indexoflonglatbit > -1)
{
htmlresponse = htmlresponse.Substring(indexoflonglatbit + whattofind.Length);
string latitude=htmlresponse.Substring(htmlresponse.IndexOf("("));
latitude=latitude.Substring(2,latitude.IndexOf(")")-3);
whattofind="Long</strong> (WGS84) </td> <td width=\"50%\" align=\"center\" valign=\"middle\">"
indexoflonglatbit = htmlresponse.IndexOf(whattofind);

if (indexoflonglatbit > -1)
{
htmlresponse = htmlresponse.Substring(indexoflonglatbit + whattofind.Length);
string longitude = htmlresponse.Substring(htmlresponse.IndexOf("("));
longitude = longitude.Substring(2, longitude.IndexOf(")")-3);

string url_to_follow = htmlresponse.Substring(htmlresponse.IndexOf( "http://www.streetmap.co.uk/streetmap.dll?grid2map"));
url_to_follow=url_to_follow.Substring(0,url_to_follow.IndexOf("\"")+3);

result = latitude + ":" + longitude+":Provided By www.streetmap.co.uk:"+url_to_follow;
}

}

}
finally
{
// Releases the resources of the response.
myHttpWebResponse.Close();
}
return result;

}
}