Hi jeffre4,
If you scroll to the very bottom of either the homepage or the 'About us' page of most sites - you'll see some small print. In there somewhere is all the legal stuff about trading names, where they're registered and whether they're FSA regulated etc. If the firm is a 'white label' and/or a wholly owned subsidiary of another firm - it should say so in there somewhere. If you do a search on the parent name - you'll soon find out what other companies are part of the group. AFAIK, here isn't a list with all this info on - not least because it's constantly changing as new companies spring up and old ones go belly up or get bought out etc.
Tim.