After some fiddling experimenting I have a solution that seems to work.
Would just like some comments please:
CODE
RewriteEngine On
RewriteCond %{REQUEST_URI} !^/folder1/
RewriteCond %{REQUEST_URI} !^/folder2/
RewriteCond %{REQUEST_URI} !^/folder3/
RewriteCond %{REQUEST_URI} !^/folder4/
RewriteCond %{REQUEST_URI} !^/folder5/
RewriteCond %{REQUEST_URI} !^/folder6/
RewriteCond %{HTTP_HOST} !\.domain2\.org\.uk
RewriteCond %{HTTP_HOST} !\.domain3\.co\.uk
RewriteCond %{HTTP_HOST} !\.domain4\.co\.uk
RewriteCond %{HTTP_HOST} !\.domain5\.co\.uk
RewriteCond %{HTTP_HOST} !\.domain6\.co\.uk
RewriteRule (.*)
http://www.mynewdomain.co.uk/ [R=301,L]
The document root contains folders 1 to 6 under which contain the site data for domains 2 to 6.
Folder 2 is domain 2 etc.
The URLs point directly to these folders.
The URL for username.hostname.co.uk points to the document root, which in turn now points to mynewdomain
The domain mynewdomain is actually domain4 on the same server.
The question is, the permanant redirect to mynewdomain is what I want for the username.hostname domain but are there any implications in terms of Search Engines and Google Analytics for the other domains ?