Having gained the Parts 1, 2 and 3 qualifications you can register as an architect with the Architects Registration Board (ARB); the title 'architect' is protected by law, so that the public can always be sure that they are dealing with a properly qualified architect.
At this point you are eligible to become a Chartered Member of the RIBA. This gives you access to a wide range of services and benefits, and entitles you to become part of, and have influence over, a national and international network of architects.