To find an architect:

UK Directory of RIBA Chartered Practices lets you search more than 3000 UK firms by name, location, area of expertise and services offered.

RIBA Chartered Members Directory lets you search more than 28,000 RIBA Chartered Members, if you’re looking for a particular architect.

RIBA Conservation Register lets you search for an architect who specialises in heritage properties.

ARB Architects Register  lets you search the official UK Register of Architects.  The Architects Registration Board (ARB) is the body set up by Parliament as the independent UK regulator of architects.