You can find out about possible franchise opportunities from a range of sources.
British Franchise Association (BFA)
A useful starting point is the BFA website. As well as offering franchising guidance and seminars on franchising, it provides contact information on all BFA members' franchise opportunities - both new franchises and existing franchises for resale.
Assess a franchise opportunity carefully and to ascertain credible franchises you can check if the business offering the franchise is a member of the BFA.