Processive glucosyltransferase involved in the biosynthesis of both the bilayer- and non-bilayer-forming membrane glucolipids. Is able to successively transfer two glucosyl residues to diacylglycerol (DAG), thereby catalyzing the formation of beta-monoglucosyl-DAG (3-O-(beta-D-glucopyranosyl)-1,2-diacyl-sn-glycerol) and beta-diglucosyl-DAG (3-O-(beta-D-glucopyranosyl-beta-(1->6)-D-glucopyranosyl)-1,2-diacyl-sn-glycerol). Beta-diglucosyl-DAG is the predominant glycolipid found in Bacillales and is also used as a membrane anchor for lipoteichoic acid (LTA). a 1,2-diacyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol + UDP-alpha-D-glucose = a 1,2-diacyl-3-O-(beta-D-Glc-(1->6)-beta-D-Glc)-sn-glycerol + H(+) + UDP a 1,2-diacyl-sn-glycerol + UDP-alpha-D-glucose = a 1,2-diacyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol + H(+) + UDP Glycolipid metabolism; diglucosyl-diacylglycerol biosynthesis. Belongs to the glycosyltransferase 28 family. UgtP subfamily.