The Architects Registration Board (ARB) hold the list of registered architects practicing in the UK, and protects the title of 'Architect'. The benefit of hiring a registered architect is that they are regulated by the ARB and you can be assured that their competence and training is of a high professional standard. However, many architectural designers have not followed this traditional route in their professional training, and this does not mean that they are any less competent or talented.
For any design professional it's important that they hold Professional Indemnity Insurance.