Qualifications and professionalism.
The title ‘architect’ is protected by law. Only people on the Architects Registration Board (ARB) register can call themselves architects. Architects are subject to rigorous training and codes of conduct; they study design for many years (it takes at least 7 years to qualify), and should be masters at creating spaces and using them as efficiently as possible. As professionals, architects are also bound by codes of professional conduct to put the interests of their clients first. The ARB requires that all architects carry professional indemnity insurance, which provides peace of mind for clients.
Architectural technologists are also professionals, registered with the Chartered Institute of Architectural Technologists (CIAT). They also have to go through rigorous training and qualifications to become chartered. Broadly speaking, technologists tend to be more detail and construction focussed, and architects tend to be more aesthetically minded, but this isn’t always the case. TOA pride ourselves on every aspect of our service.
Anyone can call themselves an architectural technician or architectural designer. You don’t need any qualifications, or have undertaken any training to do so. That doesn’t mean that they are all bad; some will have completed parts of the training to become an architect or a technologist, or may have trained as engineers or surveyors. Others, however, will have no formal training at all. As a professional body does not regulate them they have no professional obligations to look after their clients interests or to carry professional indemnity insurance.  You should always check whether your designer has appropriate insurance, and ensure that they will be giving you the level of service that you require. Always insist on a formal appointment setting out the terms of service and look at previous work before engaging someone.
See the ARB website and the CIAT website