As my host supports the IIS7 URL ReWrite 2.0 moduke, adding the following section to the primary web.config file solved this for me;
1: <rewrite>
2: <rules>
3: <rule name="RedirectToWWW1" stopProcessing="true">
4: <match url=".*" ignoreCase="true" />
5: <conditions logicalGrouping="MatchAny">
6: <add input="{HTTP_HOST}" pattern="^mydomain.co.uk$" />
7: <add input="{HTTP_HOST}" pattern="^mydomain.info$" />
8: <add input="{HTTP_HOST}" pattern="^www.mydomain.co.uk$" />
9: <add input="{HTTP_HOST}" pattern="^www.mydomain.info$" />
10: </conditions>
11: <action type="Redirect" url="http://www.mydomain.com/{R:0}" redirectType="Permanent" />
12: </rule>
13: </rules>
14: </rewrite>