[1] After his graduation Gabriel served at the Royal Electrical and Mechanical Engineers, and afterwards started his career in the construction industry.
From 1947 to 1957 he was resident engineer at Babcock & Wilcox and participated in the construction of conventional power stations.
In those days Gabriel was chief commissioning engineer for the Nuclear Power Group (TNPG).
From 1985 to 1988 he also served as president of the International Project Management Association[5] as successor of the Danish Steen Lichtenberg, and was succeeded by the German Roland Gutsch.
In the late 1980s and early 1990s he was project manager at the construction of the Sainsbury Wing at the National Gallery, and at the rebuilding of the opera house at Glyndebourne.