A C20 spokesperson confirmed that it had raised concerns over the architect's planned redevelopment of the Grade II-listed New Filton House, South Gloucestershire ( shown on right of picture).
According to the source, the conservationist group believed there was 'far too much' intervention by the London-based practice.
C20 said proposals should not influence distant views of the former Bristol Aeroplane Company headquarters and there should be a 'less intrusive' adaptation of the building's rear elevation.
The architect planned to redevelop the rear of the deteriorating building and restore its interior, to make it suitable for modern occupation.
The 1936 building was designed by H Austen Hall (of Whinney, Son and Austen Hall) and, according to Pevsner, was the largest aircraft and engine design offices in the world when built.
Horden Cherry Lee refused to comment.