The important thing for the search engines is that the link from your domain (
http://www.demosite.co.uk) goes to the actual URL of the platform. This should be done technically with HTTP code 301 (moved permanently). In no case should Javascript, META refresh, frame, or splash pages be used for forwarding. These are not liked by search engines. Discuss the technical details with your provider.
The forwarding of your domain
http://demosite.co.uk to the actual home page cannot contain any changes (for example,
http://demosite.co.uk/epages/demosite.sf). Search engines downgrade the link even if the WWW is missing.